In some instances, when you notice strange WP spikes and quite a few 'time critical DB' calls, which some are normal, but there are a lot more than normal, then bad indexes could be the issue. Y
ou cannot generalize to say that index rebuilding for performance is rare, or even medium rare, it depends on many factors, most importantly the characteristics of the application.
- In scientific applications (clinical, laboratory) where large datasets are added and removed, the need to rebuild indexes is "common".
- Conversely, in system that never update or delete rows, index rebuilding rarely improves performance.
- In systems that do batch DML jobs, index rebuilding "often" improves SQL performance.