DIR-835 here. I have LEDs on my device.
A power sign that can be green or amber.
A planet (internet) that can be green or amber.
Currently I just have the power symbol as green by default and if the router is off it'll be off.
For the planet, I have default state as off. Trigger is netdev, it's looking at eth0.2 which is the WAN. Trigger mode is link on, transmit, and receive. So basically it just flashes all the time. Probably quite unnecessary to have it to flash that much.
I haven't decided what to do for amber lights.
What do you guys do with your device LEDs?