What are pointers to pointers good for?

Question

In the Go programming language; how can pointers to pointers become useful?

(Why are they not illegal if they are not really useful?)

Answer 1

Here is an example involving ** right in the standard library:

https://github.com/golang/go/blob/cfe2ab42e764d2eea3a3339aac1eaff97520baa0/src/encoding/gob/decoder.go#L20