Think it's mostly to do with timing issues and resonance handling. The BOB's that handle slaving do some internal trickery and split/buffer and boost the signals so they arrive at the same time with enough juice.!

Slaved motors can remain sync'd but they need to be tuned correctly and run well below there limit. If you run near the limit and have half decent weight gantry and cutting hard or fast then it's easy to start dropping steps over the job period.

Most troubles with missed steps come from over tuning and running too fast losing the steps from gantry pushing on de-acceleration or sharp directional changes.
This happens more than you realise when cutting materials that need higher feeds like woods and plastics and jobs which take several hours.
Now over the course of a job these lost steps don't often add up enough to cause trouble with woods etc because of the lower resolution and tolerances required but if not homed regularly then they would accumulate and cause troubles so home switches are needed and because you can't instantly see which motor lost what with out using dial gauge etc so then easiest solution is use Home switches and square back up.

Like Jonathan I'm not a fan of twisting gantry back into square but my solution is to not bother with slaved motors and connect screws with belts so Eliminating these hassles.!!

Run the motors within there comfort zone when at high feeds and slaved screws work fine.. . .Push it and you'll encounter troubles guaranteed.!!