QUOTE (Walpurgisborn @ Sep 10 2010, 12:51 PM) 
Regarding 2, I can't imagine why mages in your games wouldn't use it, at force 4 or 5, you basically have blocked summoning for anyone but a troll, with the body to not care about the drain damage.
Edit to add
Also, regarding 1, why use the reroll rules, since at edge = dice pool is the point where it becomes just slightly more effective to roll extra, for the additional exploding dice on the entire pool, instead of merely rerolls.
Edit to add
Also, regarding 1, why use the reroll rules, since at edge = dice pool is the point where it becomes just slightly more effective to roll extra, for the additional exploding dice on the entire pool, instead of merely rerolls.
My Mistake... Slight Correction in my explanations here (Have not played a character that Summoned Spirits in a while) In general, at our table, Spirits Reroll Failed Dice using Edge for Binding; They add Dice using Edge when being Summoned... This generates a Dice pool for the Spirit that is generally equal to Force x2 (IF Force > 3); with Summoning benefiting from Exploding 6's during the summoning, and Spirits enjoying re-roll of failed dice for Bindings.
As for why you would not see a Mage roll the Knowledge Skill each and every time... This particular Knowledge Skill is considered a Complex Action+ (Skill Use), as the attendant action to Appease may indeed take some time, and Most of the Mage players at our table do not always want to lose time performing a ritual to appease a spirit when they are being shot at... And some Mages do not really summon anything much above a Force 3 Spirit anyways due to Magic Attribute Limits/Drain Limits. Force 3 is pretty respectable for most things (No Edge Expended, Generally)... when they want the Mojo, they Summon and Bind the Spirit... which is often very interesting indeed...