I think a lot of them add a lot of flavor to what otherwise might be a bland "diet" meal.
For soy sauce, it's extremely high in sodium, which tends to cause water retention and bloating in a lot of people, not to mention a cause of high blood pressure... Stick with the low sodium variety and in moderation.
I love fresh salsa as a condiment and use it on a lot of things, and will make my own frequently (it's lower calorie and less salt than any packaged brands)
My facvorite mustards are honey mustard and cranberry mustard - both are outstanding and give some life to a plain turkey wrap.
Tabasco or hot sauce is essential on eggs or egg substitutes...