Recently, I have submitted an early draft of a report summarising the results of a year-long project at my university, to my advisor for review. We have met up for a review of the paper, and he pointed out my frequent use of the word "we" in the paper. He considered it a mistake and asked me to change everything to a third-person view.
Personally, I found this incredibly strange. I am in the field of mathematics, and based on other papers and publications in math, it is very common and even considered "good" language to use the word "we" in writing, especially in proofs and discussions of results. For example, instead of
This proof demonstrates Theorem 3 to be true
it is considered desirable to instead write
We have thus proven Theorem 3.
The reasons cited for this preference, I have seen, is due to both convention and to avoid dodgy writing (third-person wording may suggest that the authors did something, but it could have been taken from somewhere else).
I have seen different questions on this site pertaining to this issue. This question, for example, has answers which suggest to take reference to the style guide provided by one's university, which unfortunately mine does not have. The accepted answer deals with economics, so I am unsure it applies in mathematics. This question suggests it is good to use "we" in mathematical and scientific writing. A quick search on Google, however, apparently suggests it is always undesirable to use first or second person pronouns in academic writing (see this site).
Thus, I am asking this question for my specific scenario for clarification. Should I follow my advisor's advice, or should I discuss with him further? Again, I find his advice rather odd and I definitely prefer to be able to use the word "we" as I please when appropriate.