1
general::
Very likely or obvious, self-evident, as in Needless to say, the availability of assault weapons is closely connected with crime. Although nonsensical at first glance (if unnecessary to say, why say it?), this phrase is generally used for emphasis. It originated as needless to speak in the early 1500s. Also see GO WITHOUT (SAYING).
American Heritage Idioms
2
general::
Phrase(s): needless to say
It is so obvious that it doesn’t need to be said, but.... • Needless to say, I should have spent more time on the report, but I just didn’t have it.
McGrawhill's American Idioms And Phrasal Verbs