I was on a team that did three week sprints separated by a one week “do whatever you want” while the manager and tech lead planned the next three week sprint. I lived for those weeks! It was great for fixing bugs, refactoring for the hell of it, or adding new internal features. I probably learned the most during those one weeks, because someone would inevitably refactor something and we would all learn from the approach. Sometimes we didn’t even commit the new code, but would steal successful patterns for future code.
Sometimes, we would “invent” something novel and truly impressive that would open doors to future features that were previously impossible.
We were involved in the planning, but the tech lead and manager were dealing with the details and priorities from stakeholders. So the last/first couple of days were usually us giving feedback on their plan. But it actually worked out quite well. We were a small team (4-5 of us total), so there was constant communication and no dictation, but someone had to order the cards around and keep things organized.
Sometimes, we would “invent” something novel and truly impressive that would open doors to future features that were previously impossible.