Not every tail call is for a loop.

You can have a set of mutually recursive functions, which tail call each other.

In C you can write state machines using "goto" (the implementations with "switch" are typically much more inefficient), but in languages with guaranteed tail call optimizations you can write a state machine where each state is a function.

In general, it is frequent enough to call another function as the last step of a function, even when there is no recursion involved. It is quite stupid for a compiler to use a CALL in such instances, instead of using a JMP. The only problem is that the function calling convention must be compatible with this optimization, while traditionally the C language used an inefficient calling convention that is not compatible with optimizations. That convention is a residue of the time when functions could be used without being declared and it should never be used by modern compilers.