Can all-in-ones double as Monitor?

[amd6502]

I've always thought all-in-1s were a terrible bad and wasteful idea; looking 5-10 years out, I imagine these ending up in a landfill, after either the system gets to be outdated or the mainboard starts failing. Indeed, I think this is the fate of many Apple products unless the waste is more carefully disposed of.

I took a peek at one of today's all-in-1s, from Dell, and I was pleasantly surprised to see an HDMI-IN port.

http://www.dell.com/en-us/shop/productdetails/inspiron-24-5475-aio?sf89407192=1&appliedRefinements=402

So, can this double as a display then??

If so, how does one switch between video-in and the computer? (I see a small button next to the power button; is it Reset switch? or Video input toggle?)

http://i.dell.com/sites/imagecontent/products/PublishingImages/inspiron-24-5475-aio/desktop_inspiron_aio_24_5475_module-6.jpg "1. Power Button | 2. HDMI In | 3. USB 3.1 Type A | 4. USB 3.1 Type A with Power Sharing | 5. USB 2.0 |6. Audio Out | 7. RJ45 10/100/1000 | 8. HDMI out | 9. USB 3.1 Type A | 10. USB 3.1 Type C | 11. USB 2.0 | 12. 3:1 SD Card Reader | 13. USB 3.1 Type A with Power Sharing | 14. Universal Headset Jack"

How common is it that all-in-one's can work as displays?