In this ever changing world, people leaving in this digital age are quite impatient. Browsing a slow site can irritate them. If a website suffers from slow speed or high load time, it is quite possible that visitor immediately left your site and switch to competitor's site.
At first, we have to find out what does “of them all” refer to in the title. Did I mean WordPress, Joomla and other open source CMSs, or proprietary CMSs? Well, I meant both.