I would normally stir my slow cooker meal once about 1/2 way through. You lose a lot of heat and extend the cooking time when ever you lift the lid, so you aren't meant to do it often.

We are having slow cooker bolagnese sauce with pasta tonight. If I let stuff simmer on the stove I always end up cleaning up a heap of splatters and or burning the bottom of the dish, so I use my slow cooker!