The Humanity gain for Banishing doesn't apply to easy conflicts (the roll is only available if the Demon's Power is > the Sorcerer's Humanity at the moment of Banishing).

Think of it as a matter of putting yourself at risk for the integrity of the universe. "Risk" is only risk, from the universe's point of view, if the demon who will be pissed off if you fail is bigger than you. Banishing littler demons doesn't impress the universe. [1]

If the Demon's scores have been penalized dice via physical damage, those penalties do not affect its actual Power score rating if a Humanity Gain roll is earned. Conversely, using Punish actually __lowers__ the demon's power score temporarily (rather than __penalizing__ it), which affects the dice used for a Humanity Gain roll.

Example 1:

Joe the Sorcerer is facing off against a 15 Power, 15 Will demon and his Humanity and Will are both 5. If Joe manages to inflict nine dice of physical damage penalties on the demon, his Banish roll (excepting Roleplay bonuses and ignoring snapshot rules) would be 10 dice (Humanity 5 and Will 5) vs it's 12 dice (Power and Will penalized to six each). However, if Joe succeeds, his Humanity Gain roll is still 5 dice versus the demon's unpenalized 15 Power.

Example 2:

Joe decides to use Punish instead of physical attacks, and manages to succeed with a nine-dice Punish. Joe's Banish roll (excepting Roleplay bonuses and ignoring snapshot rules) would be 10 dice (Humanity 5 and Will 5) vs the demon's 21 dice (Will 15 and Power lowered to 6). However, if the Banish suceeds, Joe's Humanity Gain roll is 5 dice vs. the Demons punished-down-to-6 Power.

In other words, using Punish doesn't help as much with the Banish (lowering only one of the two scores involved), but by rejecting the inherent "Otherness" of the Demon via this method, you're giving yourself better odds on the potential Humanity Gain roll (since the roll itself is against a lowered Power score.)

Other the other hand, using pure violence to give yourself an edge in Banishing a demon works very well for the Banishing itself, but in no way makes it easier to succeed at the Humanity Gain roll. [2]

This is because Punish lowers the power while what physical damage does is actually penalize the scores. That is, if you have 3 power and 1 penalty, you do not have temporarily 2 power although effectively you would roll two dice.

Typically, the only way to pull off a several-hours Banish and getting full-dice is to Contain the demon first. [3]