Hi. If a mage knows the possession metamagic technique can he use it to possession a regular person like a guard who is not using astral perception or astral projection??

If not then what good is this metamagic technique?? Can you give me some examples of its use??

MITS pg 76

The possessee must be astrally active to possess. Same rules that spirits are bound by.

Fun trick #1: feeding deepweed to the groups troll adept of doom ™
Fun trick #2: Make the group invisible so that the enemy mage decides to astrally percieve to spot them, then possess, even better if the targeted group has an adept with perception instead
Odd trick #1: use a ghoul as an expendible distraction

Possession is only useful against things that are astrally active.

So that can mean:

[1.]Possessing the Hell-hound/Bogie/Cockatrice/whatever.
[2.]Have your spirit/elemental/watchers/ally attack the enemy mage's focus, while hovering behind him with a held action to sucker punch him as soon as he astrally percieves to engage the spirit.
[3.]It's an especially annoying way to discourage the 'Dual-Natured' surge effect.
[4.]The teammates of the possessed enemy might not know that he's possessed. It's a great way to get insider information on the team. "Hey guys, what's the name of the scientist we're after again?" or get the drop on them "Can I see your assualt cannon for a second?" or "Oops, I accidentally tripped the switch on our 10 pounds of CXII."
[5.]Even after you turn hostile, the host's teammates may be reluctant to fight their friend.
[6.]Physical damage inflicted on the host stays with the host after you leave.
[7.]Just because the possession contest has to be single combat doesn't mean you can't have a half dozen astral weenies gang-bang him down to 9 boxes of stun before you start.

Unless you've got really high willpower to soak the deadly drain, and really high sorcery [or HtH] to knock your opponent out before he can turn off astral perception, it's probably not that great a power. Might be good for astral munchkins like projecting drakes, though.

OK. Assuming that a mage has a familiar/ally spirit from an initiation and the mage knows the possession metamagic technique can he voluntarily possess the familiar and use its materialization power to affect the real physical world??

You have to have a body to possess in order to use possession power.

And regarding the deadly drain... Trauma Damper! Every magician's best friend (of course, being an albino gnome with maxed out willpower helps too...)