For context...I was in "backyard" judo for many years before these Brazilian yahoo's came to american shores. "Backyard" means we did our throwing on packed dirt in a backyard...when it rained, on the living room floor. We had two guys break knee-caps, multiple, multiple, multiple wrist injuries (even with proper ukemi-waza), and many ribs crack when bags of water slap the ground at rapid velocity, and more than a few hyperextension injuries of knees and elbows.
I start on my knees now, or straight from position drills, because I'm too danged old & arthritic to want to be tossed hard to the ground anymore by guys who lack control or a clue. Incidently...the injuries I've sustained training throws and rolling have never been from senior students, but always from beginners. I'll occasionally start upright in good-guy/bad-guy drills, but aside from that, I prefer to start closer to the ground.
Regards,
Dave