Suppose we want to prove a result $R.$ In the process of proving $R,$ we have a biconditional $P \iff Q,$ which is true by observation and doesn't require an explicit proof taking up space.
However, to prove $R,$ we only really needed $P \implies Q,$ which is also obviously true by inspection, and therefore a proof was not given for it.
In such a situation, is it better to write (stylistically) that $P \iff Q$ or $P \implies Q ~ $?
An arrow that points both ways means an "if and only if" statement - which means it has more weight to it than an arrow that points one way. I'd prefer to use an arrow that is directed to my final destination (avoid meddling with both-ways arrows that require more explanation, unless trivial or are part of the proof). To conclude, it depends on the level of triviality/ sort of question:), but if it's enough to use an arrow that points one way in order to complete your assignment, why bother with the two sided one.
