Every database will, over time, require some form of maintenance to keep it at an *optimal* performance level. Purging deleted rows, resequencing, compressing, managing index paths, defragmenting, etc. is what is known as OPTIMIZATION in mysql and other terms in other databases. For example, IBM DB2/400 calls it REORGANIZE PHYSICAL FILE MEMBER.
It’s kind of like changing the oil in your car or getting a tune-up. You may think you really don’t have to, but by doing so your car runs much better, you get better gas mileage, etc. A car that gets lots of mileage requires tune-ups more often. A database that gets heavy use requires the same. If you are doing a lot of UPDATE and/or DELETE operations, and especially if your tables have variable length columns (VARCHAR, TEXT, etc), you need to keep ‘er tuned up.