Is there a rhyme or reason to fender clearance beyond simply clearing the wheel, or is it just up to personal preference?

When I installed fenders on my Trek 7100 many, many years ago, I installed them as closely to the wheel as possible, with barely a few millimeters of clearance. The only downside I ever saw to this was hearing minuscule rocks that would get tossed up between the wheel and the fender and the sounds that go with it until the rock was shot out the other side.

Well, I got a new bike that will take the same fenders. Since the new bike costs far more than my old one, I don't simply want to throw the fenders on in the same manner if there is actually a better way of doing so.

So, should I install them as closely to the wheel as I can, or should I actually leave quite a bit of clearance this time around?

I looked at bikes with fenders pre-installed by the manufacture, and there seemed to be a very large clearance between the wheels and the fenders, but I am not sure if this actually means anything.

I do realize that I simply prefer the look of almost-no clearance between the wheel and the fender, but I don't want to ruin anything prematurely, either.

Thanks in advance!