Long and short tends to be a confidence thing for me.
So for example, lake fishing - I want my bait pretty close to the lead or feeder. Particularly using a hair rig, that should then emphasise the bite.
On rivers though - sometimes I'm sure that fish will attack the feeder itself, whereas on other days the fish back off. So I like to have an arrangement where I can extend or shorten the distance between the hook and the feeder, and from experience I can tell you that on some days, there's definitely a "sweet spot" where bites come quicker. I would usually start at say around 2 feet long, but would go up to four or five to experiment.
(And on some days on the wye, I've been catching loads of chub on a shorter hooklength, then extended it and found I've started catching more barbel, leading me to believe that the chub are much closer to the feeder and the barbel are hanging back a little....)
I use the enterprise tackle adjusta stops to do this, expensive they may be but they do function really well and I've not had any problems with using them on 12lb daiwa sensor.
