Two things that come to mind:
- springs settling in over time
- fine tuning compression/rebound/etc to suit street driving/track/etc

I know that lowering springs on OEM struts or replacement struts will settle in over time and may drop a few more mm, but I'm not too sure if this is the case with coilover springs.

With the second point, I remember only adjusting the coilovers I had in my old car once or twice a year, mainly playing around with the rebound on bumpy roads.

Most people might just set and forget if they were getting coilovers for street duties only.

__________________
2015 Forester XT Premium
2020 VW Tiguan Allspace
teejay: If I wanted a comeback Id wank in front of a fan