I group my lenses together. I have many lenses, because I shoot a lot of different things over a wide variety of situations. However, I am becoming more specialized in my photography, so I will likely sell a lot of my shorter focal length lenses:
16-35L, 24L, 35L: This group is fun to take on not necessarily landscape photography, but scenery photography, especially in Pennsylvania where we like to go, or out west, etc. Compared to my 24L and 35L, I don't really like the IQ of the 16-35L, but I like the shorter focal length flexibility.
50 primes (own the 50L, 50 1.4, 50 1.8, over several years of accumulation
: Just a great, convenient focal length for any type of shooting situation. A 50 always goes in my bag as a backup lens.
85L: Excellent lens at all apertures, for just about everything. Love it.
100 f/2: Indoor sports lens. Love it.
24-105L: Good general walkabout lens. I have good enough glass however, that I can say this is my lowest IQ-wise performing lens. Dislike it.
135L: Indoor sports lens, portrait lens. Love it!
180L: macro lens, my only macro lens, and will never sell it. I absolutely love it.
200 f/2L: Amazing lens for anything, including indoor sports, flattering portraits. CANON'S BEST LENS.
300 f/2.8L: Must have for me, sports lens.
400 f/2.8L: Must have for me, sports lens.
100-400L: I like the versatility, but don't use it much. Will likely sell it.
70-200L: My everything lens, mainly sports on the 1D Mark IV but love it for everything! CANON'S BEST ZOOM LENS.
I will most likely purchase a 24-70L II lens. When I do that, I am selling the 35L, 50L, and 24-105L lenses. I am also going to sell the 100-400L zoom lens. If I feel I need to go more specialized for sports yet, I can sell my 85L and use an 85 1.8 if I want to. I'm still working this out.
Future purchases will include the 600L II lens, as well as any future 200-400L zoom lens, if it's at least f/4 or wider.