Other than a shorter length (which may or may not be an advantage depending on where it's used) I can see none
However I do love them
I own a Ruger #1 in 9.3X47R I am VERY fond of. I also have owned several other #1s in other calibers and also a few Sharps rifles.
Of course, one class of SS rifle that I am sure is not being referred to here, but is none the less popular is that of muzzleloaders.
I make them.
To me the classic flintlocks and some of the cap-locks of 150 to 250 years ago were the classiest rifles ever made.
But that’s just my opinion.