Myself, I have at times substituted fish sauce for salt in dishes in need of depth, or for soy sauce when I don't want the dark color.
I once had a Thai-inspired salad of grapes and apple pieces with a sauce of fish sauce and raw garlic. The grapes were probably ok, but the apple cubes absorbed so much garlicky-fishy flavor as to be inedible.
I don't mind fusion cuisine in principle. In practice, though (around here anyway) we seem to get dishes with inscrutably long lists of ingredients. It's impossible to predict which will predominate in the finished product and which will be undetectible. It seems like a real chef would have the judgement to do his experimentation on his own time, and not on the customers who are paying top dollar. It's a waste for me to pay a premium to be some would-be chef's taste tester.