Sometimes (for example a random fire animation) looks better, if it is not allowed to play one frame twice (if the animation has more than one frames). Sometimes a frame is playing 3 or more times - this generates an unlovely delay in the animation.
Example: after frame 3 from [1,2,3,4,5] is played, it is not allowed to play the frame 3 again. The next frame is a random frame from [1,2,4,5]. I hope you understand, what I mean.