I do a mixture of venue sizes. I play with so many people the consistency of kit just isn't there, so the idea of using ears just doesn't appeal. I don't fancy getting stuck somewhere where there aren't enough mixes, or the monitors aren't up to it, or (or the PA in smaller gigs).
It's not exactly a hardship to carry backline around, and if you choose wisely it'll be an easy lift , and sound marvellous.
IEMs are clearly the answer to many, but not all.