Why is runservice used in cframing, cameras, and etc.?

RunService is used a lot in cameras and CFraming because sometimes the client (aka a user) isn't always running a stable 60 frames per second or the same framerate as you. With different frame rates, the animation you make could last 5 seconds while it could last 50 seconds for someone else. The reason RunService is great is because you can run a piece of code to counteract that delay per frame so an animation runs exactly the same for everyone regardless of the framerate condition.

You can read more about RunService here: http://wiki.roblox.com/index.php?title=API:Class/RunService