Many years ago I reviewed a pack that had extra-long straps. They were almost trailing along the ground as I walked, but when the wind caught them, they whipped me around the head, and my ears were raw with the abuse. I wrote something like... "flagellation on the fells is not one of my vices"... but the editor cut that bit out, which was a pity.
I chop them off, along with all the other modifications I make when I buy a pack. In an extreme case, you can chop a pound in weight off a pack and leave it in better shape than when you bought it! Approach the job with care, because if you cut it badly in the wrong place, you can cause irreparable damage, and the manufacturer won't be interested in putting it right for you! You'll probably find that the best way to cut a strap is to do it on a firm surface with a hot knife. Yep... get an old knife and heat it in a gas flame until it glows... then simply melt through the strap. OK... some materials won't work this way... so test a bit at the end of a strap before committing yourself to anything more drastic. Another method is to cut the strap with a razor-sharp blade, then briefly pass the end of the strap through a flame to melt loose fibres and stop them fraying. Again... do it with caution... testing a small sample first. If you can't do it with a hot knife or flame, then you'll have to do it the old-fashioned way by cutting and sewing up the ends to stop them fraying.
It should go without saying... but try and imagine your pack at its fullest capacity... and make sure you leave enough straps to be able to secure and adjust as necessary.
