In the time before wireless, we used copper cables to get connected to the rest of the internet. That worked fine, until WiFi made us lazy cable-hating internet consumers. If you need cable connection, then the cat6 should be inside your walls. But preferably you shouldn't have any cables at all. And if you're living in a house where you can't do cable management inside the walls, there are special ethernet-via-power-outlet appliances you can get as a workaround.
I don't trust those appliances. They are lousy. But I needed a wired connection to my Raspberry Pi and NAS, which just happened to be in the other side of my apartment, some very-far distance from my router. How do I do that?
Well, I could ignore the fact that cables are an eye sore, and condition myself to not see a potential cable running along the walls (or across the floor, most likely). But I'd probably never hear the end of it whenever someone came to visit.
I could move the devices, although that wouldn't be much fun.
I could try to fit the devices with WiFi. Finally, an idea which seemed promising! The Raspberry Pi could run a wireless adapter, and then bridge that via the ethernet port to the NAS. The speeds would be terrible, it would be rather unstable, and it would not support any additional network devices... but it would do the job.
Finally, I looked around and purchased a €10 wireless router which I then hooked up as a client to my existing wireless network. The configuration bridges the 4 ethernet ports with the rest of my network. It's not as cheap as using a cable, but it's a pretty inexpensive solution anyway. I haven't benchmarked the speeds, but
I haven't run into any issues thus far with it :).