In some ways it's mostly like using any other consumables to help get the job done, but with the added benefit that you don't have to visit the AH to stock up on something that may be out of stock.
I'm sure we could contrive some more expensive use scenarios for the ammo, like an exp party or intentionally not wearing your QA or TA gear, or purposely not using Temper II, or using it on trivial parts of content.
I imagine a W3 Dynamis boss, group depending, could eat up a lot more than 200k.
And then there may be jobs whose access to Multi Attack is lacking and for them maybe it'd be more expensive, not having as much TA to cut the procs in half (but those jobs probably also get a bigger percentage boost in TP gain for it)
But it's easy enough to pick and choose when and where you use it, and a person could just pick one or two Basement bosses out of a whole Sortie run, if they wanted.