Yes, I did on a trip last month. You're right, it doesn't really save much time. You still have to go to the kiosk to print your luggage tag, then get in the line to drop it off. The only thing I noticed was different was that when I scanned my boarding pass at the kiosk, it had auto-filled in the bag(s) I was going to check. So I guess maybe that saved me, like, 30 second, lol.
When I did the digital bag check offered in the app, I did notice the language said "click to reserve your baggage tag(s)." Maybe I'm overthinking it, but I found the use of the word "reserve" interesting. Made me wonder if there would ever be too many checked bags and Southwest would have to limit how many baggage tags they handed out for a particular flight? Please note that's my own musing, not something I've actually heard (from SW or as a rumor).