First of all - three things? I charge the Apple Watch watch every day, my phone every other day or so, sometimes more.
That's like one or two a day.
I guess you might mean a laptop, but it's not like you really have to remember that generally since it just gets plugging in when I get home to attach to a larger external monitor. But that would still be three at most.
Anyway, as to why the Apple Watch is useful - it's just handy.
There's not one thing that's amazing. But It's nice to see notifications a little quicker, and to know they were important enough to make it to the watch instead of just the phone. It's just a little quicker to see who is calling or messaging me. It's just a little quicker to respond to people. It's just a bit nicer to be reminded to get up and stretch every hour or so instead of getting lost deep in the fog of the computer.
It's many little things, none of which are amazing as I said - but together they are enough that I find the device worth carrying with me, and am sad if I forget to wear it for the day.