In fact so far as I know, St Trina's Sword and Torch are the only sources of limitless sleep in the game, all other sources require nonrenewable resources. And a lot more things are susceptible to sleep than you'd expect.
It also just does a boatload of damage with high INT scaling, I'm pretty sure it had the highest raw AR out of any straight sword I owned in that run. Even without the sleep effect it would be pushing top tier vs other straight swords, and with the unique sleep effect it just blows them out of the water.
Also also, it just looks cool as hell, one of my favorite straight sword designs in the entire game.
If I were to do the build again, though, and focus straight swords rather than focus DEX/INT and just happen to land on a straight sword, I'd probably build it to be either a guard counter or dual wielding build. A 1h SS doesn't do a whole lot for you in combat. It's not heavy enough to stagger people reliably and it's not high damage enough to just delete them before you have to worry about incoming damage. Guard counter solves the former and dual/powerstance solves the latter.