When working on a few microservices with several deploys per service per day per programmer-pair, not deploying on a Friday means a ~20% productivity reduction. We had one of thosr days as there was an important demo day and our work got blocked in staging. When it finally does deploy to prod, you're exposing your users to all the changes at once and if there's an issue it's much harder to isolate the cause.

Our basic rule is don't deploy and leave any day of the week. If something does happen on the weekend, we're unofficially on-call via slack. I can only remember this happening maybe twice in two years.