X or Z. Impact has 7 seconds left but both X and Z are up. Use impact to save the proc or ignore it and keep the X and Z going?
Almost capped out on mana. Burn some with a quick E. Riposte and save the burst for a safer time, or gamble with it and try to get the whole combo in? Maybe use an E. Riposte to shift your GCD just enough to be able to make some slidecasts and double weaves you otherwise wouldn't be able to.
What spells will most efficiently get me to 80/80+? Am I able to save up to get a double verfinisher under one embolden without overcapping? Every lost mana is lost damage. Every lost second casting is absolutely 0 DPS, RDM suffers the ABC rule more than any other caster in this game. Aside from 0 DPS when not casting, RDM's resources can only be generated by GCDs. So you want the fastest mana generation possible, but want to avoid overcapping, which can be difficult because the only way to burn excess resource is in melee range.
Need to optimize Displacement. Is it safe to do now, or is healing too heavily required so displacement can't be used? Is there not enough room in here? Do I have time to fit a Displace and a CaC in before using Manafication?
There are checkpoints in fights where I need to be at specific mana, and I need to act differently depending on what level of mana I'm at. End of Ifrit Ulti, I'm at a very different point in my rotation if I'm at 80/80 and if I'm at 100/100. This can heavily shape my next 8 GCDs in Titan Ulti because of how cutthroat he is for every cast.
Make sure you cure proc every time the boss jumps so you can hit him with a free Aero or Thunder when he drops back.
Is it the most complex? No. Is it the most punishing? No (although it's not like RDM can just "get back up" after death like some pretend; losing a finisher or worse, a double finisher's worth of mana due to death is crippling in its own way.) But let's not pretend the job has no nuances whatsoever.