I guess I should also clarify that it will (usually) remember your Guardian from session to session. So if you've already set it up once, then all you have to do thereafter is strap the device to your face.
I'm not sure if mine keeps forgetting just because it intentionally doesn't always remember it (such as after a reboot), or if it "forgets" when it detects I've moved too far away from my Guardian, since I keep moving it back and forth from my (home) office to my living room.
One thing that amazed me was how accurately it can track its own position. When I initially set it up and played with it for a while, I was in my living room. I don't remember how charged it was when it arrived, but after I pulled it out of the box I played for about 2 hours before it started warning me that the battery was going to die soon. So I turned it off and took it to my office to charge up. Later, after it was charged, I put it on my head at my computer desk and it told me I needed to return to my Guardian zone. So I got up from my desk and began to walk around it so I could exit the office and go to the living room. As part of the process of walking around my desk, I happened to face where my living room was (on the other side of a wall), and the Quest 2 showed an outline on the floor through the wall of where my Guardian zone was location. How did it know where it was in relation to the living room? I turned it off while in the living room, moved it to the office and charged it before turning it back on in the office. It felt like having x-ray vision! Or like in sci-fi movies where robots/cyborgs have blueprint schematics and other similar things overlaid on top of their "regular" vision. I don't think the Quest 2 was intended to be used for AR, but that's basically what this was.
It's really cool (and kind of scary!) to think of what could be possible in a couple/few decades as the technology improves and continues to miniaturize.
Later I also discovered that you can mark the size and position of a real-world couch and desk and it will show them in VR to make it easier to sit down or place your controllers down with the headset on. So I did that. And now when I'm playing in the living room, I can see where my desk in my office is through the walls. And when I'm at my desk, I can turn my head toward the living room and see the Guardian boundary as well as my couch through the walls.