What are the pros and cons of being co-supervised?
Pros:
If one supervisor gets hit by a bus, you still have a second supervisor who is familiar with your work and can thus give constructive comments on it, hopefully appreciate it and in particular evaluate it. Often, your supervisor is the only person at your university who is actually capable of fully understanding and properly judging your thesis and defense.
If one supervisor turns bad or turns out to be bad and for example gives bad advice, makes ridiculous demands or even expects you to do questionable things, you can still turn to the other supervisor for advice or to have a serious word with the bad supervisor. If the relationship to the bad advisor goes totally awry, you may have the option to drop them and be supervised by the other supervisor alone.
It depends:
You may be expected to do more or less work. For example, if you are doing an interdisciplinary work and have one supervisor from each discipline, the supervisors may only understand and value the work you do in their respective half and thus think that you did not do enough. On the other hand, they may also overestimate the work in the respective other half and thus be more easily satisfied.
You can benefit from the experience of both supervisors and learn something from one advisor that you cannot learn from the other.
Cons:
- You may be affected by disputes between the supervisors. For example the first supervisor may tell you to do something in a certain way and then the second supervisor blames you for it.
- If aspects of your work require input from both advisors, you may need to wait not only for one supervisor to have time for you but for two. This is in particular difficult, if you need to talk about something with both your supervisors at the same time.
Some of the above obviously depends on the details of the relationships between your supervisors and the reason for the co-supervision. Thus, you can only judge yourself, if these points apply to your case and how important they are for you.
I was co-supervised (one of my supervisors was the former supervisor of the other supervisor, making me my own academic uncle) and also want to do a pro and con list:
Pros:
- When one supervisor was away, the other might still be available. So I probably got more supvision than I would have otherwise.
- I could complain about one supervisor to the other if things were going badly.
- I got two slightly different points of view on everything I did, which was certainly valuable.
Cons:
- One of them left part-way through my thesis and I was not allowed to switch universities, even though I was mostly working with the one who left by that stage.
Wrzlprmft's answer is very detailed, and this just serves as my personal experience (since I am doing just this: my Master thesis is supervised by 2 tutors with similar application areas).
If one supervisor gets hit by a bus, you still have a second supervisor who is familiar with your work and can thus give constructive comments on it, hopefully appreciate it and in particular evaluate it. Often, your supervisor is the only person at your university who is actually capable of fully understanding and properly judging your thesis and defense.
This! It is not uncommon for STEM PhD students to do internships or a semester abroad at another institution (this actually happened to one of the supervisors at the middle of my thesis). Having 2 supervisors just gives you the chance to present with the one remaining.
You can benefit from the experience of both supervisors and learn something from one advisor that you cannot learn from the other.
As far as why one would go to the extra trouble of having 2 supervisors think of it as follows: you are able to learn from different PhD students, that can have slightly different fields. In my personal case, one of them is clearly more into physics and engineering concepts and prototyping, while the other is very knowledgeable in computer simulations, programming, etc. This definitely helps!
My piece of advice after having done such a project is (as in most project management):
- Try weekly/biweekly meetings where everyone is present.
- Send important updates/pdfs or questions via email with everyone as CC. (Keep in mind to address in the email if you need an answer of supervisor X, as people tend to feel less obligated with this approach)
Best of luck in your project.