Enabling the midi channels only really alters what is shown in the instrument list, rather than actually disable them.
It would certainly help tidy things up though, and help prevent you from addressing the same midi channel with two instrument definitions. But you can still change the midi channel in the parameters anyway.
Personally, I keep a pretty close eye on what channels I'm addressing, so haven't bothered to disable any midi channels per instrument.
Until now, that is... thanx for the tip
mr o