Whistle while you work II

Buy the new book, "Beaucoup Arlo & Janis!"Today's "Arlo & Janis!"
An interesting discussion yesterday about “might could.” I wrote it that way, because I’ve heard people say that all my life. I probably would not have written it that way had I been writing a more formal document, but I was writing dialog. Conversation. Plus, I don’t remember, but I can guarantee you I was in a hurry; I didn’t pause to think about it being a colloquialism. If I had, I probably would not have written it that way.
True, the words “might could” form something kin to a redundancy, and one correct way of asking the question would be, “I thought maybe you could get coffee.” In defense of the colloquial, I ask, What’s the big difference?