2 parts
Cache
Is like a buffer that sent to a users machine.
So they dont have to pull down the information again and again.
Sometimes to see the results you require
we clear the cache to get the most up to date results.
If there was no cache everything would run slower.
But your ok to clear the cache when you want to see
any changes you may have made in the cp.
So its a clear cache and page refresh
Example : if i changed the number of say members to appear as
top posters, viewed the main index again they may look
the same as previously.
But clear the cache forces you browser to get the latest
information from the cache
Hope that helps.