I'm with you on the funeral. I don't recall every wearing a suit to one. I'm going to pay my respects, not to style on folks. I'm sure I'd feel different if I was playing a bigger role in the event. Parent, sibling, etc. Until then...
I'm talking more about business. What happens if an opportunity becomes available, but this key person you need to meet is going to be at this formal function. It's your best chance to meet him. The event is tonight.
Or whatever the situation is. My point is that you don't need one until you do. Why not be prepared?