I don't mean to be critical, but the questions seems like asking -- should I buy a bus or a truck? Seems like the answer is entirely in whether you want to haul people or things.
Someone pointed out that if you have a 70-200, the 135 would seem rather redundant. On my 1.6 crop I use a 60mm for macro (and some classic portraits). I use the 135 for candid portraits, my first love.
As big brain said the 135 is not so good indoors, houses for example. But it would be okay in an auditorium or large meeting hall or ballroom. It's also unobtrusive at sport events and it's speed is great for stop action and background control. I've used it on a tripod to shoot dance recitals with good results.
The real value of the 135 for me is the candid portrait. Especially on a crop frame it keeps me far enough away from the subject that I don't become a distraction or part of the story. I don't have any problem with mounting a 50mm and sticking the camera in someone's face but I lose the purity of a candid portrait when I do. And I do talk with people after shooting them because the picture event has an intimacy that should be properly acknowledged.
For me, as a walkaround lens, I use the excellent efs 15-85. When I go to events and want good candid portraits, the 135 is my only real choice. And to get the spider on that flower, the 60 macro.
Anyway, if you're hauling people around, get a bus. If you're hauling potatoes, get a truck.