In any case, shouldn't the clips keep tempo even without enabling beat snap?
Not necessarily, if the clip's actual duration is not exactly the same as a multiple of a frame time.
The next clip can only be started on a render pass.
The rendering runs at the frame rate you see in Resolume if you enable Show FPS in the Output menu.
So when a clip would end somewhere between render passes, the next clip can only be launched some time later.
This can get your clips to be launched out of sync with the beat ticker after some time.
Does this make sense?