I've personally found that the higher fat the foods are that I eat, the slower my loses are.
For example, I eat 1200 NET calories a day. If I were to eat 1200 calories worth of chocolate everyday for a week then I know for a fact that my loss that week would be much less than say if I ate 1200 calories worth of apples that week. (Note that I don't recommend only eating only one food for the whole week lo!)
Of course you're going to eat food that are quite high in fat sometimes, just try and keep them in moderation and you'll be fine
There's not a thing wrong in having, say a quiche for your dinner or another typically high fat food. Just make sure you eat plenty of fruit and beg along with it.
I roughly try to aim for a little thing I can 'thirding it' which is for every 1/3 of my plate that I have a food with a fat content (such as quiche, cheese products, meats) then I try and fill the other 2/3 of my plate with non fat foods like salad, veg etc. I find this gives me an appropriate moderation of fatty/non fatty foods (after all we do need fats in our diet). I think SW do a similar thing, but I think it's more do to with their free food and syns or something like that -shakes head at that 'OTHER diet'-