Over-functioning is Not Job Security
You would think that under-functioning teams are bad, functioning teams are just right, and over-functioning teams are perfect. But in reality, team members who over-function can cause the team dynamic to change in a way that may not be the desired outcome. At Microsoft, we hire people who are driven for results and it's a competitive environment. During a project cycle, if there is a gap where work is not getting done that should be done, it is natural for someone else to step in and do the work. But if you are the person who is stepping in and over-functioning, you need to be careful.
One of the biggest flaws in this approach that I have seen is that the over-functioning person thinks that they can do the work when, in fact, they aren't qualified to. Then, although the work is getting done, it's not done well. This not only causes problems for the team, but for the over-functioning person who expected accolades for doing extra work is actually seen as causing more issues. If you are going to over-function, do so within your skillset and experience level. And be honest with yourself about what you are capable of. Another consideration you need to make before over-functioning is whether you really can afford to do this. Over-functioning by doing a secondary role while you let your primary responsibilities suffer is not really over-functioning at all. You are just replacing some important work with other important work. And it all needs to get done. In this case, you need to do the job you are getting paid for. Sometimes that means that the places where there are gaps in the work may cause failures to occur which may be major issues for the project cycle. But exposing these gaps is much more important than covering them up by over-functioning. This is especially true if the correct people aren't being held accountable for those gaps. Over-functioning just makes it less apparent that the accountability is misplaced. Now I'm not saying you should stay within the confines of your immediate role and watch the project fail around you. It is best if there are gaps (in people, funding, skillset, etc.) that you escalate and/or communicate to the correct people to get this fixed. This solution is better than over-functioning, not to mention your work-life balance will be much better!
Over-functioning is not the same as innovating. If you need to do extra work to stretch your skillset and move your career in the right direction then by all means, do it. Exploring new technologies, prototyping and doing proof-of-concepts, and creating new tools to improve overall efficiency and quality are all good things. That is innovation. You may need to work more hours to make this happen, but the benefits to you are even greater. Innovating can gain you much more job security than over-functioning ever will. Over-functioning just hides problems, creates new ones, and causes you to burn out. So be careful in the extra work you take on and remember that overdoing something doesn't actually mean it is better.