For the full series see http://tale2tell.com/premiere-pro-tutorials/

The 'Posterize Time' effect can be used to set a frame rate for a piece of footage or a nested sequence. However, in this tutorial Andrew shows how to use it as a special effect to create dramatic looks for your footage or to give the impression that the footage was taken on an older camera which worked at a different (usually lower) frame rate. (Note: Although it is possible to animate this effect, it can cause unpredictable results and so any keyframes created will be hold keyframes giving instant transitions rather than gradual changes)