With 11 or 12 speeds on the cassette, in ranges of 11 to 50 tooth cogs, you get an adequate range for speed and/or climbing. You do have gaps in between cogs with large tooth difference, but sometimes that's OK. You skip having to figure out what cog to go to after you've decided to go to a different chainring. In some cases, such as mt. biking with a lot of short and sharp up and downs, you're just banging thru the rear quickly and it's really easy. Some folks state that no front derailers means less maintenance and that's true, but it's not like front shifting suddenly got really bad or harder to maintain. Indeed the Shimano Di2 systems make front shifting precise and accurate and easy to use.
I love 1X on my mt. bike as the description above is exactly what I ride, I have little need for the "in between" gears. I would not want it on a road or gravel bike as I desire the closer jumps between cogs that a 2X system give you. YMMV.