The current election interface advises:
You should only rank the candidates you think would make good moderators.
I see two potential scenarios, both of which are dissatisfying:
The STV system is strictly implemented. In this case, this is bad advice. For example, if I think all candidates would make good moderators except Alice and Bob, but Alice is the lesser evil, I should rank Alice before Bob (but after everybody else). This matters if and only if all other candidates except Bob and Alice were either eliminated or have already won a seat. In this case, my preference may cause Alice to win the remaining seat instead of Bob – which is how things should be.
SE does not strictly adhere to the STV system, but may under some circumstances consider how often a candidate was ranked at all (as opposed to where they were ranked)¹. In this case, this would need clarification how this information is used, and many other guidelines on how the voting system works are inaccurate, etc.
¹ This would have to happen manually as OpenSTV should not deviate from the voting system.