Except that the DogTag library has simply astronomical resource usage. If you can avoid using it, I would highly recommend doing so.
Currently I have only one addon that uses DogTag: InfiniBar, which uses it for customizing keybind text and button highlights, for some reason. As I'm looking right now, DogTag alone is averaging 4.7 CPU/sec.
For comparison, I am running a total of 158 addons (including libraries); my addons in total are using an average of 12.5 CPU/sec -- that means that DogTag alone is using 37% of all the CPU time used by 158 addons, and that's with only one addon using it for very minor tasks. If I disable InfiniBar and DogTag (and Rock and the other libraries that are only used by IB), my addons in total are using 3.9 CPU/sec -- less than DogTag alone.
CPU usage is by far the biggest impactor on your game's performance. For s***s and giggles, I just disabled the InfiniBar crew, and staring at a wall got 141-147 FPS. I re-enabled InfiniBar and its libraries, and staring at the same wall (I didn't move the camera) I got 133-138 FPS. I can only imagine the greater difference if I were using addons that used DogTag more intensively.
In short: if you don't
need the level of customization offered by DogTag via CowTip, don't use it.