This tiny script takes the selected layers, sequences them with a frameoffset of 1 frame. Then they get precomposed. It activates the 'Time Remap' property and adds an expresion to it.
This expression is bound to slider. With this slider you can now switch the displayed layer. The benefit of this is keeping your composition tidy. You can have hundered of layers in a precomp and just select the one you need to be displayed at the time.
Also you can add more layers to that precomp and the expression will be aware of that. It takes the number of layers to set the range of the slider.
get it over here --> aescripts.com/timeremap-source/
see the help pages over here --> fabiantheblind.github.com/timeremap-source/