Most egregious problems with MacOS X are solved by running File System Check (fsck -fy) from the command prompt in Single User Mode. In certain other rare cases, Disk Warrior, will recover lost files. However, routine maintenance is automatic, for the most part. OnyX will not hurt anything because it merely wraps a GUI around certain UNIX commandline maintenance tasks. However, it is a waste of time because MacOS X executes these tasks automatically.