It comes down to game knowledge. If you aren't looking to steal stuff in general, you don't. Especially since you get them super early, -clearly- thieves can't be incredibly powerful/useful as time goes on, as you get "better" classes.
Once you realize NPCs have rare gear on them, you go full Steal-whore on any subsequent playthrough or whatever playthrough you are on, and you don't complete missions until you steal anything that isn't obviously storebought. Then you realize that stealing shit has incredibly low outcomes, so you need to try a lot. Naturally this progresses to leveling classes that incapacitate npcs or in some way make it easier to steal their shit without breaking it. So you end up with Mustadio on every map using the shot that stops movement, or the shot that stops action. But you need to level up so you get the 100% accuracy on the shot skill, so you do that. At this point, Random battles are intensely harder than anything storywise, because in order to unlock all the tools necessary to make stealing to some degree guaranteed, you way outlevel/outgear/outskill every storyline mission (sans Weigraf in the cathedral, of course). Or you use Bards and just ruin the game entirely. Mimes were neat but never nearly as neat as having 2-3 bards on a map singing the HP song, while Mustadio snipes and Ramza as a Ninja with Steal just runs around ruining inventories.
When it finally comes down, you end up abusing certain mechanics to create combos that let you do specific things consistently, and once that's in play? Random fights are so much more intense because you get Hydras and other shit randomly attacking you first for 3x your max health, so you get into weird "best possible group" situations. Groups that don't use Mustadio are just limiting what they can pull off, because being able to Snipe for Don't Act is so hilariously OP that it makes the pure DPS of TGC not matter for the meta of the game, which is: steal everything/tame everything and one-punch Altima.
And today, I started up another game of FFT because goddamn it's one of the best games ever. Bad translation and all.