Not only does it increases the risk of injury for the person being thrown, the person who is throwing becomes to afraid of injuring the uke, so the skill level of both takes a hit. The uke is afraid of being thrown, and the thrower is afraid to throw.
Sometimes I just tell the students when master goes to the toilet, "Guys, Ukemi for 5 minutes. No throwing, just ukemi by yourself". Then when master comes back he inspects every person and gives a few pointers. Ukemi should be stressed more in MA. Even if you're not a grappler, you should learn Ukemi. Knowing good Ukemi determines if you are able to next class or not.