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."
Use of word "so" undermines your credibility (Via Lifehacker)