I find the VT520 more pleasant to look at than a LCD screen. The VT has a CRT and no backlight - when its dark, the screen doesnt "glow". The brightness and contrast are adjustable via two potentiometers, allowing eye-strain-less reading during the night.

The terminal bell makes an audible beep, i use that to signal stuff happening in IRC.

Probably because its a CRT, it also doesn't inhibit me from getting tired in the late hours like a phone or laptop does.

Last but not least, the hackability: You can interface the VT via uart, and thus can use it as user interface to an arduino or other retro computers. KVM-like switches are also easy to DIY for serial connections.