Most don't matter. "snug" with an appropriate length wrench is usually both enough to prevent loosening and not so much you risk breaking anything, with "appropriate length" often what standard hex-keys and combination wrenches are produced in.

Some do, or at least "appropriate length" departs from standard wrenches.

Lots of people (including some bike shop mechanics) don't get crank arms tight enough which can result in them getting loose at which point they move, open the taper they rely on for a press fit, and are ruined.

This still applies to splined cranks which don't have separate pinch bolts - they have a slight taper on the mating surfaces (ISIS used 1 degree) with installation stretching the crank arm until it bottoms against a shoulder on the spindle.