It's ideal for those who live on battery power as it should in theory ramp down to as low as 10hz, depending on what you are doing.
Essentially there's no negative about a 120hz display. I'm sure the 'blooming' outrage that plagued the iPad Pro launch will resurface but I personally don't think it's a big deal.
pro motion is great, mainly for the battery savings. Ive honestly never felt a difference between my 120hz iPad pro, 60hz work computer, 120hz home pc, and 60hz iPhone. Some notice, some don't, some have placebo joy.