Sara you can cook a joint of meat in a slow cooker no problem I hardly ever use the oven to cook a joint except for pork 'cos I like the crackling .
For example a piece of brisket ,silverside ,topside, a chicken ,a gammon joint .Half a leg of lamb .
For beef I just put in the pot cook it on low for six hours ..bingo. It makes it's own gravy you don't need any liquid and you just have to thicken the gravy .Brisket is best as it has nice marbling of fat .You might need a little liquid for topside or silverside as it's not so fatty .But only a teacupful of stock .
Chicken ,bung a lemon and a load of garlic up it's rear end ,plonk it in and cook for six hours on medium or all day on low .Same with lamb just shove it in .Or add some cider for gammon .Or you can put vegetables in the bottom of the pot and lay the meat on top.Whichever way the meat will be really tender .You can use any old cheap cuts of meat because the long slow cooking process cooks it to perfection .
So you could use chuck steak instead of expensive braising steak for example to make a casserole .