I must admit I haven't found much of a use for the guide frame but there are those amongst us (or amongst "them") that can't keep a horizon level, so it might help them.

The other use is when you're hand holding and want the steadiest pictures possible. Conventional wisdom says that you should watch the edge of the frame as instability shows up there much more than it does in the middle. Problem is that when you're watching the edge for wobble you're missing the action in the middle, and the guide frame can take the place of the border
mask, showing you the shake.

Try it and see. Turn on the guide frame, zoom to wide-angle and track through your local maze, Overlook Hotel-like. It really helps.

tom.

I keep mine on all the time. I find it very useful not only for holding the camera level but also for framing the shot.

You're right, the "perfect thirds" that the guide frame imparts is a classic set piece for any photographic composition. I think I'll turn mine on again.

tom.