When I open my forum, I want to quickly find out which new members have joined, quickly scan what countries they're from, make sure there are no spammers, etc.
Other forums (even free ones like phpBB) make this possible without even entering the admin control panel. XenForo makes it extremely difficult to get this information (ACP => Users => Advanced Search => Sort results by).
You should be able to sort by join date directly in the members tab. Please add this feature to the next update of XenForo.