You gain the most web-building functionality if you create a self-hosted site. This typically involves transfering the free WordPress CMS to server or signing up for a web host's optimized WordPress plan. With an optimized plan, the host automatically handles backend stuff, so you don't have to worry about updating the plug-ins and CMS, and enabling automatic backups. In these instances, the WordPress environment typically comes pre-installed on the server.
It shouldn't come as any surprise that, like other web host providers, A2 Hosting's unlimited plans aren't actually unlimited. It expect you to use its service like "similarly situated customers." This is like being on a highway. If everyone is going a few miles above the speed limit, you're probably okay, but if you're barreling down the fast lane past everyone else, you're probably going to be asked to slow down.