If debug build is working as it used to, you need a PC and a special debugging program to get the logs (or access to the NAND via FTP to retrieve a system log). Also, a counted number of times, bugs or errors are impossible to replicate for testers and most users and are only popping for just someone, and the developer gave access to the debug build and the program to get these anomalies. These are far and between but has happened.
Also sometimes, literally counted ones, debug worked better than release for some users. Though IT'S NOT COMMON and it shouldn't mean everybody should use debug. But that's literally the difference between the two.