People who avoid redundancies tend to object to the extremely popular phrase “added bonus” because a bonus is already something additional. Speakers who use this phrase probably think of “bonus” as meaning something vaguely like “benefit.” The phrase is so common that it’s unlikely to cause you real problems.

More people frown on the similarly redundant “and plus”: “I was fired, and plus I never got my last paycheck.” Just say “and” or “plus.”