My first led flashlight, a Nitecore ID, didn't have a clip and never felt the need for one: thought clips were ugly unnecessary accessories!
Then I got my first flashlight with a clip and understood why people find clips handy. The thing is I kept my Nitecore in my pocket with lots of other stuff that slowly but relentlessly took off the black anodizing: my Nitecore ended up looking almost like a TI!!!
Now to be on the safe side I clip all my lights to my pocket and also make sure I don't keep metal stuff in the same pocket where the light is. I also find it handy to able to locate my lights without fumbling in the pocket.
I have to say though the XT2C is biggish, it even makes my PD31 look small so it's not that you'll to look for it much if you keep it down your pocket! If you use your TK11 without a clip I don't think you'll need one for your XT2C! : )