Super convenient if you would like to vote a few dozen times in different places, I'm sure, but that's not what it's "supposed to be" at all. I want people voting exactly once, and _only_ where they are residents, and _only_ if they are US citizens. That's the law.
It's not hard to imagine how a rural university or large manufacturing facility could sway things in state level elections if a ton of people went across the street to vote on lunch break rather then went home and voted at home after work/school thereby changing what district they vote in.
You have to prove residency (electric bill or something) and they invalidate your former driver’s license so you can’t do something like just hop across the border and get a new license because you lost your last one for whatever reason.
Some databases also include Canadian provinces.
But since voting records are public, this would be trivially detectable.
People sign when they vote and signatures can be matched against registrations. When we examine this, we don't find a large number of people performing voter impersonation.
People voting multiple times isn't really a risk, because it's incredibly stupid. It's a felony, so if you get caught, you go to jail. But if you get away with it, you've flipped one vote, and even a very close election isn't going to be settled by a couple of votes.
There were a very small handful of people who got caught voting twice in the 2020 election, or casting someone else's ballot: two or three in Georgia and in Pennsylvania. Most voted twice for Trump.
Slightly tangential, but you are required by law to get a new license when you move to a new state. And the DMV will take your old license when they give you the new one. You can move around within a state and have a stale address on your license pretty easily, though.