When Hilton started this years ago, my 1st thought was "how cool".
I used the feature maybe 3 or 4 times. After the "coolness" of it wore off, It just wasn't practical to me.

• Yea, it saves me from having to dig for a key card. I have to dig for my phone instead (I'm not one of those who's yapping on the phone constantly, so I do have to pull it out).
• On room entry, my hands are typically full. Luggage, the day's purchase, a take out meal, whatever. I'm much more inclined to drop my "key". I'd rather it be a card than my phone.
• Using the phone as your key requires bluetooth to be on. I typically have it off. When travelling, battery life is needed for GPS !! I never did get into the habit of turning on bluetooth while in the elevator.
• the card (if the door reader is RFID, which it will be if you can use your phone) is faster. Tap-n-enter. With the phone, there is a few seconds lag to communicate. As short as that lag is and as silly as this is, I feet stupid standing there.
• I seem to remember that the phone had to be held to the door a certain way. And it wasn't intuitive. And I don't remember it being consistent between properties (or doors ??).

Perhaps part of the blame for my "issues" was that I didn't use the feature long enough to learn it.
To me it was just a gimmick. I also initially tried "app check-in" and didn't care for it either, but the combo of the 2 features may some day come in handy if I ever find myself faced with a long check-in line.