benefits of

In the Sicilain Defense, the move 5... a6 usually siginifies the Najdorf variation. Many masters, however, have used it in other Sicilian variations. Kasparov has use the move 5... a6 when he played the Schvennigen variation. The dragon variation has also received similar treatment and has a been renamed the Dragondorf.

I was wondering. What are the benefits of playing 5.. a6 before the Schvennigen and Dragon lines? What effect does it have on the theory of these lines? How do you even play these variations?

Thanks in advance

In the Dragon if White plays Bc4 or not, ... a6 obviously helps an early ... b5.

I think that the main idea of this move is that it is non-comittal and flexible.  White has a propensity to castle queenside in the sicilian game which provides the set-up for b5, moving into the pawnstorm and lining up on the c-file.  a6 and b5 are a really common thread in the sicilian, so this prepares a major idea without committing early to one of the lines to you mentioned.  It also prevents any thought of Nc5, which can be annoying for black.

It, also, makes the price of using b5, for attack, a piece for a pawn or excess time to open the square.

Keeps black from playing the Keres Attack as he could against the straight Shevy, as 6.g4 just loses a pawn in Najdorf lines.

That's the main reason it became popular, and what Fischer meant when he called it a "high class waiting move."  Allows black to outwait white's most testing reply.