Yes, I "grew up" with such system. Well, a bit of a hybrid, I guess.
One of the main benefits is of course the money. Student instructors are far cheaper. Also, the student instructor could teach some "mundane work" (such as routines/steps, basic techniques) so that when the pro comes, s/he could work on the more important issues instead of using the precious time to teach steps. Ideally, we would like to have pros at our side for all lessons, and practices. But seriously, it is really quite a waste of pros' time.
And if you are fortunate enough to have a high level student instructor (let's say prechamp, champ level), then one could learn a lot of things. I was fortunate to experience such group lessons. The instructor was a prechamp latin dancer. While she is an Asian (American), she taught the class in the "Russian style": which involves lots of yelling, shouting, pushing, drills, and sweat
. I improved so much during that semester/year and I am very grateful for those "boot camps". I think some pushing really helps us to get better faster.
Of course, there is always the fear that the instructor could teach something wrong. But since they basically only teach simple things, they can't get all too wrong. I mean, a heel lead is a heel lead. You can't go way too wrong on that.