Motion trail for a layer as it moves
Using expressions to create the trail will work, but it will have the disadvantage that you will need as many layers are there are frames of the trail, and since each one will be driven by expressions it's going to get really slow.

An alternative is to make a comp with just your moving layer in it. now make a new comp with say ten of your original comps in it, and use the Animation Assistant to stagger them by one frame. Now make a new comp with this comp repeated ten or so times, and stagger then by ten frames. This will have 100 copies of your original video. If you then nested that video ten times you'll have 1000 copies, then 10,000, 100,000 etc. This should render faster because it's all based on precomps, which get cached by AE and tend to work better than separate layers.