Butter really does add something to cooking... But I'm trying to cut out animal products. When I did use butter, it really enhanced baking. When frying, I would add a little oil to prevent it from burning quickly.
Unrefined coconut oil is a nice substitute, I even spread it on toast! It may be mostly saturated fats, but they're plant-based, which is supposed to be better for you.
It all depends on what I'm making. If I'm cooking and I'll be using high heat, I'll use oil. If I'm going to slowly cook something, butter will be fine. In baking, oil will often give a moister product than butter when making cakes. It varies.
Depends on the flavor I'm shooting for. Fried eggs, butter/margerine definitely. Meats, a variety of flavored or non-flavored oils. While I do enjoy my vegies steamed and they are healthier that way I love asparagus and brussel sprouts cooked in EVOO and fresh garlic.
Thank goodness for teflon and teflon type pans that too much oil/butter/marg are not needed at all.