It happened after updating this or that CMS the whole website lost its appearance and modules failed to work.
For example, if you use modules developed for Joomla 1.5, and you update the CMS itself to Joomla 3, none of the modules will be working and you will have either to reinstall all the modules or de-update the website.
Most shared hosts overload their web servers with thousands of accounts.
During peak times, these servers may slow to a crawl.
Persons supporting website are not always able to perform back up correctly and risk losing a lot of time and customers or may incur serious financial losses.