The description says that it is "Simple setImmediate module".
And people use it (over 2kk installations). They think that it's simple and good one, but in fact it's simple and slow one. But there is no any note about it. A lot of people do not check the code of modules that they install, they expect that the creator spent time to investigate the problem to create the best decision, but it is not about this repo. The word "simple" is not the correct description, but "simple and naive", or "simple and slow" are.

Using this code in the browser leads to a performance hit. It's a fact. For some cases the impact is significant.
For example: Stuk/jszip#617

Here is the example of using of the properly created setImmediate:
https://jphpsf.github.io/setImmediate-shim-demo/
296ms (setImmediate) vs 12617ms (setTimeout === your implementation)

Node.js has setImmediate. Using your implementation in the browser is the same thing as using setTimeout, but with the misleading name.