Because I think it’s definitely a situation that will happen again (as a PhD student or as a postdoc if I elect to do a postdoc after graduation) that I will have to be both an advisee for someone and an advisor to someone else, I am writing about this because I am de facto co-advising an undergraduate capstone thesis.
My own end of the research work has not made much progress because I was writing my masters thesis; as a result I spent the whole of February with what little time for actual research being spent with that undergraduate. I may not know much about when to trust an advisee to do your work, for example, but I know I am getting more out of this masters, learning-wise, than if there was no undergraduate in my lab for a capstone thesis.
But I learned that an advisor should not have too many students, or else they will not have enough quality time with their advisor for them to be given a chance to succeed. If there was a need to cut into the time an advisor can spend with an individual student, on the other hand, an advisor should keep some time with the less advanced students. Hence why some professors may claim that they have the funding but not the ability to take on another graduate student.