There's a popular myth that Black Sabbath got a ton heavier when they started tuning down from standard E to C#, BECAUSE of this tuning. I call bullshit.
While Master of Reality, their first album recorded in C# tuning, has basically the heaviest guitar tone in the universe, and the next album Volume 4, mostly follows suit, the two albums after, Sabbath Bloody Sabbath and Sabotage, have much lighter guitar tones, despite still being in C# tuning.
Master of Reality's massive guitar tone might have SOMETHING to do with the detuning, but it definitely isn't the whole story.