Audio streams need a 32KB alignment. If they don't have it, the games crash even before sending the dvd audio command. This wouldn't be a problem, but some shrinkers, i don't know which, ignore this important "detail". If a game does not contain audio streams, then shrinking them with about any shrinker should be fine.
PS: NeoGamma has an option to fake 32KB alignment for audio streams, but it's not widely tested and it's only done for .adp files. Ikaruga for example seems to work with it, even if the game image is ruined by shrinking it with wrong alignment.