I think giving creative people some leeway to explore interesting new areas of technology is 💯 awesome. But we need to make sure that that time is being used to its best purpose: letting folks learn, experiment, and explore. If it becomes a dumping ground for tasks that don't otherwise fit into our schedules, it becomes less helpful for us as a group.
Here's a positive 10% time interaction where a developer is using their time to explore an issue that they find interesting:
Manager: So, it looks like we're not going to have time for task T123456 this sprint, and it's a low priority, so let's put it back in the backlog.
Developer: Actually, I think it's a really interesting problem. Do you mind if I work on it for my 10% time?
Manager: No problem, but we're not going to have it be a deliverable for this sprint.
Here's a superficially similar interaction that doesn't give the developer the agency to determine their own area of exploration:
Developer: I have too much to do this sprint period. I can't do all this.
Manager: Hmm... what if you do T123456 during your 10% time?
Developer: Well...
Manager: Didn't you say recently that this is a topic you're interested in?
Developer: Yeah... I guess.
Manager: Great. That means we can get everything done during this sprint period.
Here's a last one we should watch for:
Developer: I have too much to do this sprint period. I can't do all this.
Manager: So, I know this is asking a lot, but could you skip your 10% time this sprint, so we can make our deadline?
Developer: I skipped it during our last sprint, though.
Manager: You can catch up after this sprint. This is our big push. Think of what a cool big project you can do with all that banked 10% time!
Developer: OK, I guess.
I'm sure we can all imagine what happens to "banked" 10% time.
Anyway, I think we need to be very proactive in protecting this time.