Use of filler words seems to be proscribed as bad or incorrect, yet they also seem so common that they are part of spoken language. Whether desirable or not, are there grammatical rules that describe their empirical use? For instance, has a modern-day William Bullokar observed current spoken language and established rules for when you begin a sentence with "so" vs "um" ("so, great job today!" vs "um, great job today!") and the order in which you can combine them ("um, so basically like, ahem, ...")
Is it bad behavior to add filler words such as "so", "um" in business speak?