Node's fs module docs contain this line (sic):

The callback-based versions of the fs module APIs are preferable over the use of the promise APIs when maximal performance (both in terms of execution time and memory allocation are required).

No explanation is provided and I could find basically no info on this.

So, why is fs's Callback API more performant than Promises API and how big is the difference?

Update: There is a relevant issue on github that I failed to find.