To be honest, the self checkouts are almost always time savers for me, but it really depends on the store and set-up.
The poorly designed machines that make you touch the screen before you can even start, scan each item one by one, place each individual item in the bagging area and leave it on the scale until the very end, use "AI" to make sure you're not stealing, and then force you to select your payment option on the touchscreen rather than just automatically detect when you've swiped/tapped? Yes, those are an abomination.
However, there are a few stores in my area (surprisingly Walmart is one of them) where they've mostly got a decent implementation. You can walk up and just start scanning. You don't even have to place items in the bagging area/scale, you can literally scan everything in the cart with that hand scanner if you want. There's probably loss prevention / AI watching you do your thing, but I don't know. I've never been stopped by it or noticed anybody else getting stopped. If I tap my card at any point, it automatically understands I'm paying now and just wraps the order up. Plus, these places usually have a sufficient number of the machines with an open corral style set-up, so that one or two people who've never seen a self-checkout machine in their entire life are only tying up one or two machines and the rest can move pretty quickly.