1. I understand where you're coming from. ( I understand the place where you are coming from.) 2. I understand what you're coming to. ( I understand what you are trying to convey.)
This line has a very common use & people use it very often. You use it when you mean to say that you understand what someone is trying to explain or what their point of view is.
2. I understand what you're coming to.
I'd say, I've never really heard of this in normal conversation and I don't think I've ever read