A binary tree is a data structure, tail recursion is used in code ⇒ what algorithm are you thinking of that can be implemented in fixed space but is hard or impossible to do with tail recursion?
tmtvl's comment at https://news.ycombinator.com/item?id=41983916 shows an algorithm that requires unbounded space.
Traversing a mutable binary tree can be done in fixed space but is not easier to do with generalized forms of recursion than with tail recursion or imperative iteration.
You youngun's have hidden behind APIs for so long you don't even know how things work.