Super wide got super popular, its just that simple. About 20 years ago lens makers began cranking out better and wider zoom lenses. But the M series was just not large enough, causing vignetting issues with these lenses. The M series is only good for wide angle lenses down to about 25mm (on Full Frame cameras) before part of the filter holder begins to block the edges of the photo causing vignetting. That 25mm depends on where the lens maker placed the filter threads in relation to the front element of the lens. Some lenses could vignette at 26 or 27mm.
In 1998 Cokin responded to photographers needs to filter these super-wide lenses by introducing its 100mm filter system with a new wider holder to go with them. Out of the box the L series holder can be used with full frame lenses as wide as 20mm. But this holder is modular, meaning it can be taken apart to remove filter slots, going from three filter slots out of the box to just two or one slot. This allows the filter holder to be lower profile so it can be used with even wider-angle lenses. When two slots are removed the L series holder can be used with FF lenses as wide as 17mm.
The filter slots are held on to the base plate of the holder with 4 bolts and thumbscrews. Just carefully unscrew them all and remove as many of the pairs of filter holder slots as needed. In Joshua Tree National Park I found out the hard way that it is very easy to drop and loose the little thumbscrews so I would recommend doing it at home or in the studio before going out to shoot.
If you are using a super-wide angle lens and need to go down to just one filter slot I would recommend reversing the brass bolts so they are sticking out backwards toward the camera body. This eliminates the risk of the bolts sticking out into the edges of the photo.
You might also be wondering about the three pegs, two on the bottom and one on the top, that slide back and forth a little. These pegs are to hold the adapter ring in place. Push them forward and slide the adapter ring into the slot in the back of the holder then push them back to keep them in place. This also allows the longer graduated filters to be moved up and down more freely.
So no matter if you are using a super-wide, standard pro zoom or long telephoto lens, the Cokin L series holder and filter system has covered.