I always decant my red wine as you invariably find some sediment in the bottom. I think it helps bring it to room temperature if it's been stored somewhere a little cool.
If you decant non-vintage wine (ie. cheap plonk) put a good slug of port into the decanter first. It make it taste like good vintage stuff. Most times you can get away with it but have a good story ready. Say it is specially blended for you or something.