[Baalz]

A couple more points:

1) Communion slaves *do* act by themselves if they come in the battle sequence before any communion masters have cast a spell that round. The combat sequence is deterministic, so if you're clever you can do things like have your slaves casting spells while your masters come at the end casting self buffs (which effect all the slaves). If your slaves can cast things which reinvigorate themselves (like drain life) this can be a never ending fountain of nastiness as the master casts big spells and the slaves reinvig themselves.

2) A big risk of communions is that the masters don't consider the fatigue of the slaves when they're casting. This means you can quite easily have your slaves killed by a master spamming completely useless stuff at routing enemies. Nothing quite so frustrating as loosing half your mages winning an easy fight. Consequently communions are usually best for big decisive battles.

3) The buffs conferred on communion slaves remain even if the master leaves the battlefield. This means another use of a communion is to get buffs on SC/thugs who couldn't otherwise get them. Giving a slave matrix to somebody tough, then having a couple master mages cast invulnerability, blood vengence, mistfrom etc. can make for an awesomely powerful SC with very little cost. It's particularly wicked for things which can't usually wear too many items (tarasques, Wyrms, etc).

4) Communion slaves take (significantly) more fatigue when the master casts spells which the slaves don't have the right paths for. Putting the cheapest mages as slaves is not always the best choice.