A bit surprised to see how many prefer not to sip pools. I always keep track of where there are pools, and begin my sipping activities around mid-game. If I haven't found a wish by the time I reach Khelly I always sip to try and find one, although even then I'll first try clear the Frost Caves, High King cave, and the mid level dungeons in hope of finding a wish or AoLS. I find the value in pools to be the intrinsics you can gain, and that is usually what I strive for, with a wish being a bonus. I usually strive for ~2-4 useful intrinsics at which point I stop, depending on how many pools are left. Adverse affects are usually easily handled (sickness, stat abuse,aging), but the way I see it, if I can walk away with -deth, -invis, -para, -petr, -seeinvis it frees up equipment slots for better gear, and leaves less room for error (gorgons).
For when I start sipping, I always make sure I have a form of teleport control (backup corpse stashed, if no ring), high piety to clear dooming, and a way to cure disease. Even when I don't need a wish, I always go back to pray to remove doom in case I get a lucky wish.
Of course, this can be risky - last game I gained and lost many intrinsics from drinking DF empty and ended up with teleportitis and nothing else... you just need to know when to cash out your winnings and not fall for the "one more sip to try and get -para/-petr/-deth".