At least if you tried to plug a USB cable into an ethernet jack it would be immediately obvious that it wouldn't work. In today's world the wrong cable will plug in to the wrong port just fine, and you can be scratching your head for a long time trying to figure out why it's not working. And, if you are particularly unlucky, while you are puzzling it out your device can fry.
[UPDATE] Well, I stand corrected. It is actually possible to stuff a USB A connector into an ethernet socket. (You learn something new every day.) But come on, folks, telling the difference between a USB socket and an ethernet socket is really not that hard. You don't even have to look, you can do it by feel. But all these different USB-C/Thunderbolt ports are physically identical. They are literally and by design impossible to distinguish.
> At least if you tried to plug a USB cable into an ethernet jack it would be immediately obvious that it wouldn't work.
Not necessarily. Ethernet jacks are often wide enough that a USB-A plug can be partially inserted, and it's pretty common to stack the two types of ports. If one isn't looking directly at the connector (common when dealing with the back side of a tower or docking station), it's a surprisingly easy mistake to make.
I have accidentally put a USB device in my laptops ethernet port several times because the laptop is on the back corner of my desk and all the ports are on the back so the cables all go behind the desk but because of the proximity to the wall I can't easily see the ports. USB and eth are right next to eachother. Wouldn't have it any other way. Don't know what I will replace my T420s' with.
