These should technically also work on PPSSPP, as they work on a real PSP (I have one modded), and as far as I know this was a Sony format that the community uses. Similar to WAD's for the Wii and Virtual Console Injection to insert other games unofficially. PBP is the best thing for PS1 games as it compresses them a bit without needing to use archives which suck, and it combines multiple discs.
I do suggest using RetroArch with this and the Mednafen PS1 core. I didn't cover PBP's in the tutorial as I wasn't using them at the time, but I am gonna make a tutorial video at some point about Rom and Disc compression, and what the best way to do this is without using WinRar or 7zip as I think they suck for doing this job. They do do a good job for compression, so just storing these is fine. However, when you want to start playing these games then it starts to become a huge pain. PBP's, CSO's, WBFS, GCM, Trimming, all stuff that helps certain systems save space, but have it still be playable. https://www.youtube.com/watch?v=-HoXz8UyCSk