Well... as someone who has worked in an optical factory and has watched technicians stripping down and reassembling optics, I can tell you this:
There isn't a lot of adjustment in most modern lenses. The glass sits in seats in threaded modules and these screw into precise register.
Not so much older lenses, where the glass can be moved around with lens spanners in the mount to get the centring correct. With these I never take the glass out of the brass (or aluminium) mount.
So... most lenses should go back together in the same registration and alignment as they started with.
But. Big BUT.
After reassembling the optic it would then be carefully tested for alignment just to check it was within spec. Usually it was - but it is possible a foreign body got under the seat or a spec of something stopped a thread from fully returning to it's register. The other possibility is just making a mistake - leaving a spacer out or putting a shim in on the wrong side. Occasionally this would happen and mean that something might be a little out of adjustment. Often it would just mean dismantling, cleaning the thread or seat and re-assembling again.
But without the optical bench and calibration equipment - how would you spot this? You have no quality control check for reassembly errors.
If I'm going to strip down a lens I at least take some pictures of a test chart or something first - so after reassembly you can check the before and after and see whether you've trashed the performance.
Although personally, my rule of thumb is to dismantle as little as you need to to do whatever you need to do... For most jobs the problem is usually replacing lube - which doesn't require too much dismantling of the optical parts of the lens - or removal of dust, which maybe just requires a front element taking off or something.