I got told off more than once for showing initiative and pushing something forward that wasn't on the approved list for the sprint even though I had time and there wasn't anything left to pick up.
Yes, mobbing fans, I know, I could have jumped in on a story that already had people working on it. This is what management there said to me as well.
Nevertheless I'm rather old fashioned so I have two comments to make:
1) Too many cooks... etc.
2) Adding more people to a project/story that's not going to deliver on time will only make it later. (Here I'm obviously paraphrasing Fred Brooks.) And if it's going to deliver on time then why add more people instead of enabling those people to work on something else that's useful?
In the end I gave notice without any plan about what to do next but had three opportunities lined up before I'd worked my notice period and have been much happier since.