If you are training for hypertrophy you need some sets at least close to failure at least every once in a while.
For strength and athletic performance, staying well under failure is helpful. Even for hypertrophy, strength-focused sessions or blocks of sessions that stay well under failure can be helpful because the increased strength will translate to more hypertrophy once you use bigger weights with hypertrophic training. If that makes sense.
As far as total volume goes (whether total sets to failure or total sets below failure, or some combination), it really is something you've got to experiment with yourself. Some guys seem to be able to beat themselves up pretty good, recover fast, and hit it hard again soon after. Other guys have to take it relatively easy, and need long recovery times between sessions, too.
Shouldn't need to be said but strength training incorporates low rep ranges (say, sub 5) while hypertrophy focuses more in higher ranges (say, 5 and up).
There is something to be said for Dante Trudel's method of using one weight until you can rep it 30 times, then increasing weight, then staying with that weight until you can rep it 30 times, then increasing weight, etc etc. For those who can actually make it work, it seems to be quite effective.