Do you mean when using it as a relay because p2p connectivity isn't possible? The preferred operating mode of Tailscale networks is for the bulk of traffic to go p2p, using various tricks for NAT and firewall traversal.

I’ve used it extensively to stream video across continents. No issues as long as you can get a P2P connection going. If it needs to go through a DERP server, then it may suffer but in my experience that’s pretty rare.