I just prefer it as it avoids a trip into LAB processing…perhaps not such a big deal but with both versions why not. I likely would always use it post tone mapping I think if I was going to …I guess to stretch the DNR if there was still room but to that end I tried on purpose to add too much white relative and then stretch it with auto levels and then set relative white correctly . There was not much benefit if any to the look that I could see…maybe a quick and dirty way to tweak the midtone slider for a final small adjustment??
It would be interesting to see exactly how people are using levels. I think for me I would just be using rgb curves to do anything that might be done with levels??