Depending on the circumstances then animations inside QML can use considerably more CPU than when viewed normally. For instance there are two different cases of this happening but seem to be caused by the same thing.

On Windows, if you use -opengl desktop and turn on VSYNC for the graphics card then it will use 3x the CPU to render the example.

On Mac, if you minimize the window then it will use 10x the CPU to render the example.

Both of these cases are related to the animations and seem to be as a result of the timers, but it is not clear if it is because of the handling of the timers or the animations itself being handled quicker.