Sounds a bit curious from my perspective, but that's just because I don't have that habit. And as a habit considered, I don't think we need to assume it's connected to the stuttering. However, the preoccupation with what you're saying as you're saying it seems a common feature of stuttering. It just has different outcomes, I suppose. For me, it's more like thinking in "tracks" of variant phrasings, such that I can jump back and forth if I encounter problems. That's just a bad habit, though, since it doesn't necessarily give me control, and it most likely adds to my confusion during. Speaking can put quite a strain on me, incidentally, and I think it is in part because I (we) have to mobilize a lot more resources around the delivery of speech.