If you're talking about defragmenting the disk, the Apple support person hasn't read Apple's note on when it makes sense to defragment and why you typically won't need to. OS X automatically defragments files 20MB or less, so unless you need large areas of disk space available, you don't need to take defragmentation action. One reason you might want to, for example, is if you need large blocks of free space for video processing.
If you're talking about general disk optimization, which doesn't include defragmenting the disk, but does include cache cleaning and the like, there are several programs that can do that. OnyX is one I and others have used for years with no issues. Of course with any disk maintenance program, you should have a backup of your data before using it. Note that there are Apple routines that run periodically that do some, but not all, of the same disk cleanup.