I chose this pedal to save some space on the board, dual pedals offer more features in a more compact format. The left side offers a slight break-up of the clean signal, like plugging in directly onto a mixer. The right side sounds like a Tube Screamer kind of pedal, lots of sustain but still some clean sound coming through. Stacked together they sound a bit compressed, but good for a lead tone.
My only problem is that the two sides share an EQ, so if I set it the way I like the one side, the other sounds a bit too muddy or too shrill. Not a dealbreaker though.