I've recently seen beginners writing programs like this -
This is terrible practice. Why? It's very slow
compared to traditional entry / exit conventions. It saves and restores 16 64 bit "general purpose" registers, 16 32 bit access registers and the PSW. Traditional entry exit saves and restores fewer 32 bit (well the low order 32 bits) "general purpose" registers, no access registers, and no part of the PSW. Years ago, when BAKR / PR were relatively new I did a performance study and was shocked about how bad its performance was. This was before z/Architecture with 32 bit registers rather than 64 bit registers. I no longer recall the exact numbers from roughly 20 years ago, but it will most likely be worse now.
This was also about the time IBM was starting to put together the XPLINK convention. A big part of XPLINK was to save and restore fewer registers in addition to other changes to improve overall program performance in an environment where small subroutines are frequently called. Clearly BAKR / PR are not used in XPLINK.