Cleaning cache is neccesary then user updates roles, users or groups. Expire cache link cleans neccesary policy cache and ensures that user rights are updated. It's recomended for non admin users to click "Clean cache" button then administrator updates their permissions.

Clean cache link can be seen in system configuration page. Also then you are changing templates make sure you have disabled live helper cache.

'templatecache' => false,
'templatecompile' => false,
'modulecompile' => false,