I answered 'somewhat often' because, as a college course, we have 'newbies' quite often.
With our regulars, I try to keep a quiet class but I realllly tend to get over analytical after class. This gets even worse around people's testing time.
I also find that many people like to talk a whole lot more when sensei can not attend class. I feel that not speaking during class is a good thing. I've also noticed that sensei leans more toward doing than explaining to learn, though if pressed, will explain quite well.
I think that explanation only works if you've put the time into finding out the questions by practice. A person can ask, "How do you do X-Waza?" but if they've never tried to do X-Waza then no amount of explanation will make the "light go on".