My personal rule of thumb is to have fired cases land about 6 feet away when shooting from a standing position, so it depends on the load. I have spring weights from 14 to 19 pounds and it seems to get me there with light to +P pressures.
I like to start heavy and stop when the slide locks back on the last mag round...then shoot several mags full to make sure it locks back every time. If it fails once, I drop down 1# and that usually does it.
A too-light spring does two things...it'll batter the recoil surface of the receiver (unless you use a Shock Buff), and it'll allow the slide to cycle faster...sometimes too fast for the mag spring to get the rounds up in time for the slide to chamber them.
A too-heavy spring will cause the slide not to lock back on the last round, and quite often will not allow the slide to cycle to the rear far enough to eject the empty case and pick up a fresh round from the mag. Also, it's hard on the slide stop and bottom barrel lugs...it'll even egg-shape the slide stop pin hole.
There are other areas affected by the wrong spring weight, but I think these are what you're primarily interested in.
The rough numbers I've heard tossed around are 16 lbs for hardball-equivalent (230gr @ 850ish), 18.5 for +P, and 20 for most 10mm loads, all assuming 5" guns. Shorter slides need heavier springs, and longer slides need lighter springs, at a given power factor.