I did a microbenchmark recently and found that on node 24, awaiting a sync function is about 90 times slower than just calling it. If the function is trivial, which can often be the case.

If you go back a few versions, that number goes up to around 105x. I don’t recall now if I tested back to 14. There was an optimization to async handling in 16 that I recall breaking a few tests that depended on nextTick() behavior that stopped happening, such that the setup and execution steps started firing in the wrong order, due to a mock returning a number instead of a Promise.

I wonder if I still have that code somewhere…