This word has many reputable uses as a preposition, adjective, and noun. Such phrases as "by the same token," "by and by," "by the by," "by the boards," and "by and large" are tiresomely overused; the last-named not only is hackneyed but is usually a meaningless conversational filler."Bye now" and "bye-bye" are baby talk for good-by.
Dictionary of problem words and expressions. Harry Shaw. 1975.