Tail calls also matter for code in continuation-passing style (CPS). This matters for some styles of programming (callbacks/promises/monads/etc), but it's also

Tail calls also matter for code in continuation-passing style (CPS). This matters for some styles of programming (callbacks/promises/monads/etc), but it's also very useful for code emitted by compilers and DSLs. It's much easier to encode complex control flow with CPS than just with the basic constructs JavaScript supports. Even for hand-written code it can be pretty important. It's easy to imagine rewriting simple tail-recursive functions in an imperative style, but it quickly gets much harder, especially if your problem naturally decomposes into mutually recursive functions: that is, instead of a function calling itself, you have multiple functions calling each other, often with a bunch of additional computation between each call. I've run into this when writing parsers as well as custom algorithms for constraint-satisfaction kinds of problems. (Which are pretty common!)