When reviewing first posts in particular, it is my understanding that one should check if the question is a fit for the site, among which if the question makes sufficient sense. I take these tasks fairly seriously, and have recently been confused. What constitutes "low quality"?
To make this concrete, the 2 cases that prompt me to look for guidance. I flagged these 2 for low quality, and add the feedback received after my flag was declined:
vector operations between a two-dimensional and a three-dimensional vectors ("flags should only be used if a question demands moderator attention" - I would understand if a moderator thinks it is "not low quality" (although, how, I do not know, but one can disagree); but how am I supposed to understand this?)
https://math.stackexchange.com/questions/318792/a-characterization-of-probability-theory ("moderator found no evidence to support your flag" - question was closed shortly thereafter, probably as it is not an actionable question, which is why I flagged).
As said, I take my flags very seriously, and don't want to be on the record as someone who flags many unjustified posts. Reviewing first posts has an answer box "low quality", which is a subjective criterion which I took as "it's low quality, alright, flag, then let a moderator decide what to do" - but to at least bring it to a moderator's attention I had thought to be encouraged.
I happened to visit the StackOverflow voting page today, in which candidates underline their number of flags as evidence for how much they care. To understand this properly, I do not consider flagging as preparing a future candidacy (because that will never happen); but it seems at SO flagging is considered a good thing, whereas I cannot help feeling that the most recent feedback sounded as if I was told to not bother the moderators.
It seems to tell me that only absurdly bad posts should be flagged (or spam maybe). I feel disinclined to ever flag 'low quality' again, and lean towards just waving through new posts if it just leads to me having a bad flagging record.