system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: What would be the effect of having one computer connected via LAN and the rest of the computers connected via WiFi?

So lately our router seems to be working rather slow and when we've contacted our supplier the support center told us it could happen due to someone on the network connected via LAN and "taking up all the bandwidth".

I've searched around the internet a bit and it seems like unless some 50MBps downloads are currently running on that computer, the effect should be the opposite.

Is having one computer plugged to the router via WiFi and another computer connected via WiFi work faster than one computer connected via LAN and another one connected with WiFi?

**edit:** you guys are too kind. Thanks for the help!
Personally, I don't experience these problems with my PC, but my roommate keeps complaining about slow connection (he's the one using WiFi), and our internet provider asked him whether or not we have any computers connected to the router using a LAN cable, and said it might be the cause. We're leaving the apartment in a month and it doesn't really matter that much to any of us, just kind of annoying. Asking more for general knowledge since I like gaming with LAN connected and was afraid it might have an effect on other people who are connected to the network.
gpt
Depends on the router; they're not all equal, and it's not always about the bandwidth being used.

Figure a typical router's network ports operate at 1 Gigabit (1000 Mbps). A typical wireless connection is limited to approx 50 Mbps;   You could, in theory, connect 20x devices wireless before matching the bandwidth a single physical port allows for.  Now this never actually happens because wireless technologies, interference, processing speed, packet loss etc, never get you the full bandwidth. 

What's often more often the case, is the router's ability to handle multiple wireless connections to different devices at the same time is limited.  You also have to consider that the "Wireless" connection on the router is a single interface being shared by multiple devices, and splits the wireless bandwidth between them; where the physical port is just the one device. However, not all wireless routers are 'rated' for the same wireless bandwidth.  A wireless router rated for, say, 300 Mbps has to split that between all wirelessly connected devices.

Now taking all that together, and assuming your actual internet connection isn't the limiting factor;  having a plugged-in computer should have no noticeable impact on your wireless performance by a longshot unless it's a pretty junky router.  Having a computer plugged in directly would theoretically IMPROVE wireless performance, as it's one less device to share the wireless interface.