For properties that offer Digital Key it means visiting the front desk is, essentially optional the vast majority of the time. (Sure there are occasional hiccups but...) it also means most of the time I can choose the room I want rather than hoping that someone notices the "high floor, away from elevator" preference in my profile and/or I can weigh those against available rooms myself (e.g. I'll take a room on the 10th floor 4 doors from the elevator over a room on the 2nd floor 20 doors from the elevator, hands down)

I love having the flexibility -- for my most frequent property it means I can usually just park in the back, let myself in through the back door that is right next to the elevators and go up to my room without talking to anyone (there are a couple FDAs that I usually have good chats with but I can do it in my own time when I'm not just off of hours of travel and don't want to see anyone)

For properties that I've never stayed at before or stay at infrequently I'll usually do the OLCI and then when I get to the hotel if the desk isn't busy desk I'll say hi / ask if there's anything I need to know (trick elevators, room service, ...) and sometimes get a physical key cut just to avoid technology issues -- but if there's a line I can just "nope" my way past that and get to my room without having to stand around.

I almost universally (attempt to) check in as soon as I wake up the day before the stay but when I do that probably 80% of the time I get the digital key at or before check-in time (a couple properties I have more extensive experience with pretty consistently push the digital key around noon -- then follow up with a "how's your stay?" text 10 minutes later even though their check in time is 4pm and I may not have even boarded my first flight yet).

I can't remember OLCIng for UK hotels (and I seem to recall it wasn't available in NZ) but in the US, generally, the OLCI window opens at 6am local property time the day before check-in.