The first pass of a 2-pass render enables the codec to better (better = smaller file size and better looking picture) squish the material on the second pass. Whether it is worth it in terms of extra time and any extra picture quality/ file size is largely dependent on the source material (the format and codec of the native video and the nature of what effects and compositing imposed upon the native video during the editing process).
I always use a 2-pass render for final delivery BUT:
1) Time is not so critical for me: I have a powerful rendering machine and I can let it run through the night.
2) My source material doesn't get too mangled up in the editing process and - **at high bitrates/ minimal compression** - I actually rarely perceive a difference on my monitors, which are decent. For those that really, really need to eek every ounce of quality out of limited file sizes, 2-pass is requisite, of course.
See here for more info:
https://en.wikipedia.org/wiki/Variable_bitrate#Multi-pass_encoding_and_single-pass_encoding
If time is a critical factor for you and file size is NOT, then you could probably get away with churning out high bitrate single-pass renders (perhaps even at a [high] fixed bit rate where 2-pass doesn't even play as a factor) and you might save yourself some grief with a single-pass render.
h.264 (and way moreso, h.265) are indistinguishable to me from magic in how much quality they can jam *into a small file size*. It's voodoo, I swear it. But if you're OK with larger files, the renders can fly because there is much, much less work to do to achieve the voodoo or quality AND small file size.
I'll paraphrase an old saying: GOOD PICTURE, FAST RENDER, SMALL FILE. Pick two.
