Since everyone seems to be recommending ISOs, I guess I'll be the one to disagree and say ISO is a garbage format for games on platforms where CD audio is a factor. An ISO is just a binary dump of a disc's data into a file, which means it's missing vital track information. Imagine if you dumped a music album to one single MP3, and then were like "OK, I want to listen to track four." But there no longer is a track four, you just have one giant track for the entire album. Now you get to seek through the hour of audio manually and search for when track four starts, because the single MP3 doesn't know or care.
Video games which use CD audio (i.e. tons of games on most CD-based game consoles) face the same problem--if you don't provide it that information (e.g. through BIN and CUE), the emulator has no idea where the CD audio tracks are or even whether or not there are any. And an emulator doesn't have the human ingenuity to just dig through and try to guess where the track starts or anything, either. When a game tries to play CD audio, the emulator will just go "Welp, I don't have any CD audio around as far as I know. Enjoy the silence
Now, there are also a lot of games that don't use CD audio on PlayStation. Sequences, XA, some custom crap, whatever: that audio will play fine, so you might play a few games from ISO and get the impression that this is working great and you should keep doing it because it's worked out so far. But that's a short-sighted approach, and if you keep play PlayStation games from ISOs you're going to run into a bunch of really dull games which have no music for some reason, and it'll be because of your format choice but you'll probably never know it.