@kwf I used to and regretted it to no end, because (to my imprecise observations) it can cause havoc if you have a non-static machine (aka laptop) and/or VPN. So if 'fastest' changes, and DNF and the net do not agree, fun ensues. My 2cts (that may be inaccurate). I now leave it to default, and try to limit dnf in general to core libraries, with user space provided by flatpak, so less use case in optimizing it.