Flippers / Fins

What is the current thinking on flippers / fins? (ie, professional coaching recommendations). It seems like their use is very pervasive these days but when I was a swimmer growing up (US Swimming) we did not use them...and I swam with some kids that went to Olympic trials...so it was a good team. My masters team uses them ALL the time. They don't do kick sets without them. They even use the flippers for main sets at times, and some swimmers sneak them on to keep up with their lane, which messes up the lane order (and in fact they should swim in a slower lane if they cannot make the workout in the faster lane without flippers - IMO). And they use them when they are slow in other strokes (ie, IM's, back, butterfly). Some of these swimmers have mastered kicking with fins (esp those that use huge scuba fins), but they can't kick worth beans without the fins. Is there any research/articles on fin usage? What do the top swimmers do? Thanks!