[jacobmischka]

It's a compiler optimization, not something an end user should really ever use. As an end user, it should just look like a function whose final statement is the call to another function (often itself, recursively).

One may be familiar with "stack overflow" which is when a series of function calls (often recursive) go so deep before actually returning that it exhausts the maximum stack space (essentially an array of scopes containing variables/state for each function). A proper tail call will realize that it can reuse the same existing stack frame instead of adding a new one, which essentially makes exhausting the stack impossible and removes the need for the CPU to do all of that bookkeeping.

In performance sensitive workflows it can make a large difference.

[cerved]

It's broader than compiler optimization. You have to implement algorithms in such a way that the recursion is in tail position. Sometimes you may also have to specify that the function is tail-recursive (I believe that's the case in Scala?)