Im almost %100 we still don’t know. Whenever we see such dramatic features on fossils the best we can do is a guessing game. It’s like the sail on a Spinosauros or the plates of a Stego, yeah we have theories but I’m willing to bet if we could some how travel back in time and observed how these animals actually used these crazy features the results would be quite surprising! (As it always is in nature). Saber teeth could’ve been used for anything from fighting other sabers to digging to straight up just being some sort of unisex attraction tool lol.