well, here is my opinion.

it's never a bad thing to do it, but you may omit it as soon your gap between the flight control and the surface is small (on a SE).
if you do it, your flight controls will be more responsive in any case.
I use clear tape to seal my flight controls instead of using monokote. It's important that you seal such a way that your flight controls keep all the throw without heavy load on the servo. This can be a bit dificult the first time, that's why I suggest you to go with clear tape that you can easily remove for your first atempts