The obvious, HD radio (NRSC-5-D) significantly increases audio quality, as outlined by the FCC and Consumer Reports.
The stations with HD do better on lower heights and with less power, and as others have mentioned it helps with multipath.
Most importantly, the average listener cares about no static and if a signal sounds better they’ll flip to it more. They’re not actively seeking out the best audio quality but the night and day difference matters. If KMVQ dropped HD, I bet they’d start slipping in market share to KYLD.