Important virtues of a good QR system include security, speed and convenience.
The first point, security, isn\'t a major concern if you can securely screw the camera onto the tripod head, unless you didn\'t get it right, or you\'re using something heavy enough to come unscrewed when you sling the tripod-mounted camera over your shoulder to move somewhere. All \'good\' QR systems have a backup or failsafe feature that prevents unintentional release, the simple screw mount does not.
Speed and convenience are related, but vary between systems and users. I\'ve recently switched all of my camera and lens support QR plates and bases from Manfrotto RC2 (mostly) to Arca-Swiss (mostly RRS and Hejnar). The main reason is one of convenience. In particular, it\'s the RRS custom-fitted camera L-brackets that make the switch from firmly-secured landscape mode to firmly-secured portrait mode so quick, sure and \'convenient\' (i.e. no crouching down and leaning over sideways when you use the tripod head to rotate the camera). I\'ve been using Arca-Swiss (mostly RRS) for long-lens shooting for a few years, and the road map to complete the transformation was quickly drawn when I put a RRS L-bracket on my 5D - it\'s so good!
Anyway, the real reason for using a good QR system is that you have so damn many pieces of gear to switch and swap between, that the security, speed and convenience provided by a good QR system are well-worth the expense (IMO). I usually shoot with two or three bodies, with some lenses that are secured by the tripod-mounted body, and others that are secured by the tripod-mounted lens. I also often use macro rails and bellows systems. Every one of these stinking pieces of gear has a QR plate. I also have three tripods (no wait, four), and two monopods that get used with many and most combinations of cameras and lenses. Every one of these pod systems has a QR base, and so do some of the rails and \'other heads\', like a NN3 pano.
Long story - short, if you don\'t need a QR system, then you don\'t have enough gear to need one.
P.S. I\'ve stripped a few QR-plate securing screws, but never the threads on a camera body. I assume this means that the camera manufacturers are smart enough to use harder metal for the body threads than is used for the screws used to attach stuff to the cameras (clever engineers! ).
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