Well, as an outsourcer I can tell you its horrible to work with for us, not with text style, but with other things, like ctb files. I have clients that have modified monochrome.ctb. So we either edit that ctb for him alone, and mess up any other client that uses that ctb, or we leave his unmodified, and never actually see his drawings as he will.
For drawing defined things, thats ok, but for things that are in the actual nuts and bolts cad setup, editing any defaults is bad in my book.