When I vote neutral, it means that I am prepared to support either of two mutually inconsistent courses of action.
It's not just a comment. It's certainly not the same as Comment: Unsure which I also use; Unsure means that at this stage I still see a possibility that one side or the other might be right. Neutral means that I have decided that, in a sense, either both sides are wrong, or both are right.
The classic case is when an article is proposed for rename, claiming that the existing title is POV. In many cases, all of the possible titles imply some POV or other. When this happens, all we can do is to choose one of them, and redirect the other possible titles. The introductory paragraph of the article should then emphasise the other possible title(s), both to conform to the principle of least surprise and to partly balance the POV of the chosen title.
(It has been observed more than once that this is less than perfect. Christian theology teaches me that nothing other than God is perfect. Baha'i is the same, but mainstream Islamic theology AFAIK is significantly different, and regards any attempt at perfection as an insult to God. But all seem to agree that Wikipedia will have to settle for imperfection at times! (;-> )
The neutral vote is equally appropriate in any case when there are problems with either option, but there is no better option.
An administrator closing a poll can validly count this vote in support of either course of action, or disregard it, as they choose. I will support them in this.
Should two admins be having a disagreement, they'd better contact me. But I'll probably simply side with whoever claimed my vote first; If I don't, it means I am changing my vote, which is also a possibility of course!
A neutral vote could sometimes be considered a vote of no confidence in both sides of a dispute. It means that I don't consider either argument to be convincing in terms of the aims of Wikipedia, and therefore suggest that we all put it behind us and get on with the job. There is an implied criticism here that both sides are engaging in advocacy, perhaps innocently.
But at other times it's a vote of confidence in both sides. There are valid arguments both ways and it's impossible to tell which is better in terms of reader experience, so we need to move on.