QUOTE (svenftw @ Mar 19 2010, 04:16 PM)

Spirits don't materialize(/possess) when they are summoned, they manifest. A possession spirit can still manifest, so that part of the summoning wouldn't change.
But they can't do anything to you when they're manifested, even if you were astrally perceiving during the ritual, you'd stop immediately once you passed out, and then it has to possess something to do something to you, which, if you're in your magical lodge, leaves it with somewhat limited options once your stand-by sprit has possessed you. I don't know though, I still think it's better to bite the drain and summon a high force spirit for a mission than actually risk death when binding it. Sure, the drain's going to hurt, but it's not going to outright kill you, and with a decent drain pool and bound task spirits with first aid, you can definetly bring drain down to manageable levels, even down to nothing. Plus, you'd
never summon a high force spirit in combat or when time is an issue, situations like that call for lower force bound spirits who, while not
quite as broken as a force 8 summon, can certainly make you the equal of any street sam. When you did summon a force 8, it would be at the beginning of the day or any time when you'd definitely have enough time to get first aid afterwards. Then you'd keep it on standby, at which point it's just like a bound spirit 'til the end of the day. Sure, every once in a while when you and your task spirit rolled extremely poorly and the force 8 rolled rather well you'd have to deal with 5P or so on your track, but more often than not it would be more like 1 or 2, well worth it for +8 to all your physical stats and an increase of all your mental stats to 8 and 16 ITNW.
And considering that a topic of interest so far has been the comparison of materialization spirits to possession spirits, lets look at the benefits a force 8 materialization spirit would give you has compared to a force 8 possession spirit.
Advantage of Possession spirits 1) Possession spirits can wear armor and have weapons
A force 8 possession spirit can wear armor fitted for whatever it's possessing, adding usually about 6 to its armor and as much as 18. How do you put armor on a materialization spirit? Are you going to use a service to get something fitted for an Aztec Guardian Spirit in the form of a Jaguar? And even if you do find armor that fits, how long is it going to take to put it on the spirit everytime in materializes? In the case of weapons, a materialization spirit, depending on its form and your tradition, may be able to carry a weapon if you carry one around for it and give it to him when he materializes, while you could either do the same for the possession spirit or have it use whatever weapons the body it possesses uses.
Advanatage of Possession spirits 2) Possession spirits almost always have higher attributes
Considering that guardian spirits tend to make the best combat spirits (IMO, not really a debate point), I'll use that for my example. In any situation where a possession mage is fighting living creatures and has a spirit as powerful as force 8 under his command he will be able to possess one of his enemies and gain its attributes, weapons, and armor. Sample attributes for guards given in SR4a gives them Body, Agility, and Strength of 3 and a Reaction of 4, 5 points higher than the stats of a materialized guardian spirit. And this advantage only increases with the power of your enemies. In a situation where a mage is fighting mechanical enemies, a possession spirit's options are more limited. While it's certainly possible for a spirit to possess a drone, the chances are a bit too low to rely on them in combat. In this situation, the materialization spirit has an offensive advantage, it can materialize and take the weapon you provide for it to deal effective damage against drones. But a possession spirit has a defensive advantage, it can possess you or your armor to make you virtually immune to a drone's bullets while you assault the drones with lightning bolts, and honestly, spells are really the better answer to drones than materialization or possession spirits anyway. Finally there's the magic opposition, which can take the form of a spirit vs spirit battle, a mage vs spirit battle, or an astral form vs spirit battle. In spirit vs spirit, it ends as either a tie or an advantage for the possession spirit, it will either have higher stats on the material plane than a materialization spirit or equal stats on the astral plane. This pattern persists for astral forms, who will have equal stats for astral combat. In a mage vs spirit battle, the spirit will possess the mage and win by jumping out a window and unpossessing before the fall. Seriously, I don't care how much you've buffed your intuition and willpower, they're still not 16. A materialization spirit in this situation gets hosed by a stunbolt the turn after it materializes because it can't take anything out on the turn it enters battle.
Advantage of Possession spirits 3) Possession spirits have mind control
Self-explanatory and mentioned earlier in this thread, a possession spirit takes out one enemy when it enters the battle. A materialization spirit has to take a turn materializing before it can do anything, and any enemy you meet is going to have a whole lot less trouble mowing down an energy being than his own ally. If your opponents have the means of taking out a force 8 spirit, at the very least they'll have to take out one of their allies too when you're using possession spirits.
Advantage of Possession 4) Channeling
A mage may use his possession spirit to buff his own stats, something that materialization spirits have no equivalent for. This can mean better mental stats for drain and a higher magic rating and more physical attributes for dodging and taking bullets, not to mention ITNW thrown into the bargain. This is something that materialization has no answer to and the main reason why possession is always a better option for summoners.
Advantage of Materialization 1)
Materialization spirits don't need a body or an object in order to appear, they just do. At lower forces and against drones this advantage is at its greatest. A summoner can summon a number of force 3 or so spirits onto a battlefield and have all of them be effective without having to worry about finding bodies for all of them. Of course, in most battles this is just going to mean a whole bunch of disrupted force 3 spirits, but it's a tactic. This also becomes important for utility summons, such as when you want to use search or something else which requires mobility. However, in most cases a well prepared possession mage can carry around prepared or natural vessls that even a low force spirit will be able to possess and gain the same benefit as a materialization mage would. Besides this, materialization spirits don't have anything that makes them a better choice than possession spirits.
I haven't seen anyone bring up anything that would justify preferring a materialization tradition over a possession tradition. Please, please, prove me wrong.