Have you also encountered the situation when your Moodle site is upgraded from a previous version and contains a lot of redundant users and courses which are clogging up the system, if so then this forum thread is of many helps to you. Started by Greg Bird the forum thread discuss about the positives and negatives of going with a clean install on upgrading the site.
Some potential issues which are problematic during the upgrade process are:
- Upgrade process failure,
- keeping a track of custom code,
- all plugins and themes also to be upgraded simultaneously, to ensure that site is working without any breakage.
You can also post your views and experience about going for the upgrade process or a clean install in the forum thread here.