QUOTE (Yerameyahu @ Nov 30 2010, 11:38 PM)

It has upsides, too. Be glad that there are also downsides, for once.

Yes, a spirit that can't go Astral is missing a big chunk of functionality, but it depends on what you need it to do in the first place.
As far as PCs go, I can't see what they would need an Ally spirit to do, that couldn't be done with a Ma. Ally spirit. The Ma. spirit gets to choose one form during the ritual, so that form could be what is "needed". Not trying to be difficult, but all I really see are downsides

*edit* downsides for PCs using In. Ally spirits, that is. I def. see opportunities for NPCs here.
QUOTE (Seidaku @ Dec 1 2010, 01:16 AM)

A 'True Form' result is basically a Materialization spirit, but with more prep work. Both the hybrid and flesh forms, however, grant some powerful advantages that neither Materialization nor Possession spirits have. Flesh form is, in my opinion, probably the best result. You get to keep all of the skills, powers and cyberware that the vessel had, but with all of the added perks the spirit brings. Unlike every other type of spirit in the game, a flesh/hybrid form inhabitation spirit can make use of cyberware and AR. Plus, with the right vessel, you could also add a ton of pre-existing skills and powers to the table that the spirit might otherwise lack or have to pay karma for. Also: Aura Masking is huge. It gives you the benefit of two metamagic abilities. It gives your ally spirit the ability to appear to be completely non-magical, which is otherwise impossible. Imagine, say, having an ally spirit inhabiting a ring or necklace, and being able to completely mask its aura. You can walk around with a powerful magical ally and no one save extremely powerful magicians would be the wiser. Don't get me wrong- being limited to just the one vessel is a major downside to inhabitation as opposed to say, Possession, but it can be extremely powerful given the right set up.
Of course, if you're just going to have it inhabit something boring like, say, a sword- then yeah; it's not a great pick (mechanically) compared to your other options. Still, it does open up cool roleplaying opportunities- an ally spirit inhabiting a sword is a way to, in Shadowrun, duplicate your 'intelligent magic weapon' fantasy trope. Inhabiting a cat, raven or the like allows for your classic magician's familiar. Sure, mechanically you'd be better off going with one of the other types, but they might not have the flavor you want for your ally spirit. Plus, ally spirits aren't just for players- the GM can have his NPCs have ally spirits using the Inhabitation power in the ways I've described to add flavor and memorable scenes to the game.
Couldn't the Ma. Ally spirit form be a sword, or necklace, or whatever, in the same way? I guess your point on Aura Masking is a really good one. But is that the ONLY upside? Oh, and using the cyberware of the vessel, but that starts to lead into the territory below, I think.
QUOTE (Jaid @ Dec 1 2010, 05:45 AM)

pretty sure while in the process of being inhabited, they are incapacitated, no?
This is how I'm thinking - In. Ally spirits using kidnapped / killed bodies seems the work of evil NPCs, not our heroic PCs

Tables may vary, of course. But if so, why restrict PCs from being insect shamans or the like?