Over the years a number of camera manufactures have done two models of the same camera, with different sensors.
Nikon used to do this the most with higher resolution and lower resolution versions of there D2 and D3 professional cameras.
Leica are now doing this with the SL2. With close to 50 megapixels its quite a beast, but for say weddings and wildlife or video, a slightly lower number of megapixels, faster response and smaller files to edit; you could say less is more.
This is where the SL2S comes in. Its basically the same camera but with a 24 megapixel sensor and faster performance and more optimised video.