So how does that work, then? Quick release plates are very convenient once the camera is mounted, but fixing the camera to the plate can be fiddly in the first place. If you're using a simple ball head, a quick release plate could really slow you down. Ball heads are easy to 'spin' when they're slackened off, so screwing on/unscrewing the camera only takes a few moments anyway.
Quick release plates are useful with three-way or pan-and-tilt heads, though. These don't 'spin' in the same way as ball heads, and normally the camera has to be attached using a knurled screw on the underside of the mounting plate. Quick release systems can be a much more convenient alternative here.
With the Manfrotto head shown above, you slide the front edge of the plate under a projecting lip and then the back edge is clamped down by the sprung lever on the left. Other systems may use parallel grooves where you slide in the quick release plate from one side.
Basically, if you want to keep taking the camera off for handheld shots and leave the tripod where it is, a QR head is fine. But if you want to attach the camera to the tripod and leave it there, they won't save you any time.
