I think it's more like a sign post in the text. At the start of any paragraph (or sentence, really) the text may go literally anywhere--could be a new thought, a continuation of an implicit list, an explanation of what came previous, or anything else.

If you say something weird or apparently unsupported, the savvy reader at that very moment is going to be thinking so. So it's helpful to orient them like:

> Here's a wild sentence. Here's why it's not actually that wild: reasons

Without the connecting phrase, the reader has to figure out from context that out of all the possible things the following text could be doing, what it's actually doing is explaining the previous claim.

You can rightly counterpoint that it's not strictly necessary, that a savvy reader can figure it out. But I think the moment right after a wild statement is a hotspot for readers getting ready to jettison, and having a little assurance is likely very helpful.

Language is filled with those types of phrases, the one which bugs me once it was pointed out (even though I use it myself) is "to be honest...", which could carry the implication anything said without that qualifier may be dishonest. What including those phrases seem to come down to is an informal style, a bit more acceptable in a spoken conversation but for written it probably depends on the audience.

Something I'd wonder about is if usage of it has changed based on the medium people use over the years, whether that's in-person, telephone, writing letters, or computer/smartphone writing. Has using computers for short form conversations allowed conversational phrases to bleed into formal writing.

You also explained what you were going to explain here

Reminds me of Mark Twain’s advice to writers, “Any time you want to write ‘very’ write ‘damn’ instead so your editor will remove it.”

> It turns out that if you're writing an essay or a youtube script you don't have to tell me that you're going to explain something to me before you explain it to me.

I do if I'm looking to pad the essay or video to make it longer.

That jumped out to me because you see it in YouTube videos so much now. I was surprised at the age of this post.

If you're writing a YouTube script, just, stop. They're so tiresome.