Single assignment

In my earlier question about immutability, most answers assumed immutability meant only ``immutability of composite objects'' and not immutability of bindings.

So, what are the advantages, if any of single assignment (or, most accurately, run-time immutable bindings)?

I can't think of many other than ``I'm going to annotate this variable cause it really shouldn't change and if I accidently mess up I want the compiler to tell me''

Surely there are other reasons.

Algol 68 has immutable bindings and syntactic sugar for mutable (ref) bindings. With immutable bindings, it's possible to simulate call-by-reference and call-by-name using only call-by-value because you are passing the value itself and not a new instance or copy of the value.
string s1 = "Hello, world!",
string s2 := "Hello, world!"
The first uses = but the second uses :=. Here, the variable declaration for s2 is syntactic sugar for the identity declaration ref string s2 = loc string := "Hello, world!". The loc string is called a generator, which creates a reference. s1 does not allocate any storage but s2 does. Parameters are always passed by the immutable identity declaration.
The identity declaration can give an identifier to a "subname" of a mutable value.
ref struct(int x,y,z) s = heap struct(int x,y,z) := (2,3,4);
ref int x = x of s;
x := 7
Now s is equal to (7,3,4).