well, I think if the singer wants screaming take in the higher level he must train, and not go for pushing harder above the limit, this can cause problems in long term. But as long I do warmup and warmdown, I do screams according to my comfort zone, if my voice starts to wear, I know when it´s enough. I happen to experience the oppositte of what I experienced in past. In like two month ago, I couldnt sing properly with full clean voice after grit/ screaming excercise. another words said I could sing but with restricted voice, now surprisingly what happens during session is I do the same or even higher amount of screams in less time, my voice gets cleaner and fuller in the middle of session, I start on heights and then I sing with clean voice or raspy with no hardship at all. this is a good sign. It seems like screams clear out the mucus left behind after nasal flushes and post nasal drip that bothers me in morning and after almost each meal. I found something interesting I feel making very slow transition into another kind of scream (false cord scream) There are actually 4 types of screams, fry scream, false cord scream, death scream, and "the rock scream" (for example Bulletboys, Sebastian Bach in younger age) what teaches Jaime, in his low grit/mid/high scream excercises. the big issue for me is the proper transiton because I want to develop softer kind of scream that allows perfect transition between 100% clean and 100% gritty/raspy. I also plan to work hard on clean voice and power soon in a couple of weeks before hitting the studio.