I can't speak for DSM or sitdown machines but as far as a LA is concerned, I wouldn't be without a stitch regulator. But I learned using one and only quilted without one in a classroom setting. Speaking only for LA I think a SR reduces your learning curve considerably. You can focus on movement and technique and not worry about keeping your stitch length consistent. The quality of the stitch regulator makes a huge difference as well. Many lesser quality ones and after market ones could very easily be more of a distraction/hindrance than help.
The base SR that came with my innova was great but I upgraded to the lightening stitch early this year and wow what a difference. It is super responsive, I no longer get a slightly longer stitch when going from a dead stop into a quicker motion, I have a much larger selection of stitch lengths from a basting stitch all the way up to something like 20 SPI for micro work and the regulator controller is now on the front of my machine head instead of at the back. I love my lightening stitch!