It will give those packets priority on upload (send them before others if there is congestion). How well that works and how it impacts the rest of your network depends on how your router has implemented it.
For download it wonât really do much, some routers attempt to delay incoming packets to other devices in hopes that those devices will detect congestion and throttle back, but in my experience it does not work very well, it really needs to be done on the other end of the connection.
Another thing to keep in mind is that enabling QoS on many home routers impacts the hardware forwarding and can impact your total internet speed and latency, so it is something you have to try and see how your router deals with it. Could end up capping your total internet speed.
Long story short, unless you have congestion that is causing impact, QoS likely will do more harm than good. I do multi-layer QoS all day at work, but thatâs on enterprise Cisco routers where I control both sides of the link.
At home the only need I have for it is when I do occasional huge uploads to Onedrive. Usually, it is not capable of maxing out my 300M upload since ondriveâs servers throttle, but sometimes they do let it hit that. In that case, Iâve just configured the onedrive app to limit to 250M so it wonât choke out other stuff Iâm doing, so donât even need the router for that. Though Ubiquiti does have quite powerful and granular QoS, just havenât really needed it.
Real world example, I set a family member up with Ooma years ago. I think at the time her cable internet was like 50/5. Both downloading and uploading files would cause the phone to get choppy and cut out. I tried various settings in the routerâs QoS and even the built in one in the Ooma box. It helped quite a bit with file uploads, but did very little for downloads.