My rule of thumb is if you're adding an effect to make something sound better, remove it. If you're adding an effect for the creative aspect, leave it.
Something like a delay might be very specific to the sound that you want and someone mixing your track might not think to add a delay like you would. If you added a delay to vocals because you think it makes them sound better or it hides imperfections, I'd leave that off. If you want to distort a sound a specific way and used a processor to accomplish that, you'll want to leave that also. If your sound is distorted for whatever reason and you tried to fix it somehow, remove that processor and explain it to the mixing engineer.
You can also export both all of the dry tracks and send over a rough mix that you did. That way, your engineer will have a good idea of what you're looking for.