If you examine your tradeskill buffs, some of them will use power, but instead of using, 49 power, whatever, it says something like 3% power. So no matter how large your power pool, it will use 3% of it each time you use the buff, so if you have a tiny power pool, you have very little power for it to take away, and your drink will make it so you pretty much regen more power than you use.