Because missing three days of velocity will definitely cause your growth hacking to fall off the hockey stick and reduce the tempo of your disruption of unique hackathons for people with a left little toe deficiency?
The changes are pushed and working in staging, the tests are passing, Q&A is done. Why hold off? So that you get your Good Practices™ badge? I'd say it's better that you don't have to deal with last week's work on a Monday if at all possible.
I think being down to earth, and keeping your good judgement is key. I don't recommend making world-shattering changes on a Friday, but even then, well, it really depends on the circumstances.
* It's the holiday weekend and your new website with its curated comparison feature needs to go live
* It's the end of the quarter and having this is the only way you can sign a deal now (enough of your partners will be bound to quarters that this is possible)
* You're in the business of live sentiment analysis from TV video and a critical bug needs to be fixed before this weekend's Presidential Debate or your news channel partner will be pissed
Reduce the tempo? Some of these can kill.