I advise pinning users to carefully measure the supposed performance improvement, as there is a tangible risk of spending time on imaginary gains.
With no pinning they'd randomly go into the milliseconds -- with pinning it would stay in the micro second range!
The result of this is games (and likely audio) performing much more favorably.
How much of this is cache coherency/in-fighting, scheduling, or simply host usage; I couldn't tell you. I was just happy to have my VM 'feel' native.
There will always be a benefit with pinning vCPUs on the same NUMA nodes as their devices (VFIO or even SR-IOV). This is becoming increasingly important on hypervisors
PMC data at scale is pretty clear: very often, CFS won't do the right thing and will leave bad HT neighbors on the same core, leading to L1 thrashing, or keep a high-level of imbalance between NUMA sockets leading to degraded LLC hit rate.
I correct my statement with "_did_ a good job", and appreciate rigorous testing.
I worked on a project where we collected detailed production runtime characteristics and evaluated scheduler algorithms against it. Tiny improvements made for massive savings.