I've found that on some mechboxes that the selector plate pushes on the right side bushing and makes it difficult to feel the axle/bushing. Removing the plate clears the path to change out the bushing (plastic) or bearing and install a metal bushing.
I use one of MadMax's tools to set the bushings square to the mechbox shell...and it can't be done with the selector plate in place.
To remove the selector plate, I remove the cutoff lever...
You certainly don't HAVE to remove it...just a consideration.