As far as players I've coached I've never said do it either way. If they took it off I taught them how to do it properly and if they didn't I just left them alone.
With that said I caught thru 10th grade then moved to center where I stayed. I never took my mask off and that was the old school mask over the backward helmet type. I don't know if it's because I was a receiver in football and you can't remove you mask to catch a football or not. But I don't ever remember the mask obstructing my view. Recently I put on one of those hockey masks and holy crap you can't even see the mask part. It actually made me a little uncomfortable because I didn't feel like my face was protected lol. I'm not arguing one way or another I just personally never thought the mask impeded my ability to catch a ball.