I sometimes start my sentences with, "So, …" (any episode of Gweek will be full of examples). But it irks me when other people do the same! Consultant Hunter Thurman gives three reasons why the word "So" sucks: It insults the people you are addressing, it undermines your credibility, and it "demonstrates that you are not 100% comfortable with what you are saying."
Rather than just plainly answering their question, you're relying on the crutch of a practiced blurb. Usually, whatever follows "so" is a carefully crafted sentence, evolved over many iterations and audience reactions.
There's a reason we do it. In psychology, it's what's known as a "marker." It's a little cue to our cognitive mind that says, "Quick, call up that part that we practiced."