mesith

So I was just wondering if you really need to have the companions that you find in-game in your party. Because I have already created my own party members and would like to stick with these but I get a feeling that the companions you find can unlock sidequests or things like that and I wouldn't want to miss out on that.. So my question is if it's really neccesary to have these companions in your party while you travel or can I stick with my own companions without missing out on anything special??