I never look at my router’s lights. I use 192.168.0.1 or whatever to do stuff in the browser.

(There is actually an option on mine that lets me turn off all the lights. (Except the power on light, dang it!))

There are only two lights that matter to me: power and WAN. They let me see if there are problems that I can't do anything about through the browser UI. If there's no power, then obviously its a hardware problem and if there's no WAN then its an upstream problem that I cannot fix myself. All other lights are meaningless to me and I use the browser UI instead, like you.

It's useful to quickly check whether the connection is 100BASE-TX or 1000BASE-T.

I've just bought new xerox printer with wifi feature. No display, just couple of leds and buttons. After half an hour and numerous google searches I was able to use it over wifi, but only 2.4GHz. Spent another hour trying to set it up with 5GHz. Now it is connected via USB only and I am happy.

I have a router with a lcd display... I never use it (the display), because well.. it's a router, and it's hidden (literally) behind a couch.