Nobody uses it. Ignite is 110% better for “going aggressive” and anyone who doesnt go aggressive (janna, soraka) is better off taking barrier because they die the moment they get in range to exhaust someone.
Also with the amount of true damage and ignites in the game there’s no point in taking it since it has no effect on true damage since true damage is counted as “fixed damage” rather than “ignoring resistance damage” for some reason.
The only time i see exhaust is for some cheese bullshit on midlane bruisers like yasuo and irelia since they dont even need ignites damage to kill someone (which is not the intended use for exhaust.) And yuumi because yuumi is an extemely special case.