Does Shamir's Sharing Scheme make sense if k=2 and n=2?
Except for the extensibility (being able to latter add a third user), the trivial scheme with XOR works just as well as Shamir; the trivial scheme retains the following properties:


The length of each share is still as long as the original secret (in fact, you don't need to bother assigning share identifiers, which you have to with Shamir's scheme)
It is information theoretically secure.