The subject of training fixes comes up regularily on here and I tend to go with the advice from D and D themselves.
They want students to use it , so that they get a clear understanding of what capabilities are on the other end of the R/T. They also realise that if people have used it before, they are less likely to be intimidated by it and use it as necessary. It gives them something to do and helps keep them sharp.
Any "professional" pilot who has a problem with this, is daft IMHO. It may be annoying occasionally, but no person has ever died from annoyance, whereas plenty have from ignorance. I know a few people who owe their continuing existance on thios planet to relays on 121.5. I'm only grateful that the crews of the airliners that passed on their messages were listening out, rather than getting het up and turning it off.
Turn it down if it gets in the way, but turn it back up again afterwards.
To the idiots who use 121.5 for chat purposes, please hand in your R/T licences, because you don't deserve to keep them.