Comment by niobe

But this is the point. What your neighbour's are doing greatly affects the performance of your network.

If you have a good connection and are successfully able to transmit packets to your AP at 600Mbps, and your neighbour has a poor connection and is transmitting at 6Mbps to his AP at that moment, you literally have to wait ~100 times as long for a free medium before you can attempt to transmit. And that's for every single frame. Then you have to hope his client is well-behaved enough not to transmit while you are transmitting. Otherwise you end up having to wait again and retransmit anyway.

You might not notice this with only 2 clients. It might be the difference between a 80MBps and a 50MBps download for example. But it decays exponentially with the number of clients.