Is the meaning of the phrase "Not for nothing" literal, or idiomatic, and if idiomatic, what does the idiom mean? If you have a reference more reliable than urban dictionary, please share it. Here are two quotes using the phrase in which its meaning seems literal:
Not for nothing had he been exposed to the pitiless struggles for life in the day of his cubhood, when his mother and he, alone and unaided, held their own and survived in the ferocious environment of the Wild.
It is not for nothing you are named Ransom.
However, this phrase comes up all the time in Aaron Sorkin's writing, especially the TV show The West Wing, and its usage there seems more idiomatic. For example:
Not for nothing, but, you know, we're gonna have to get into the thing at some point.
Josh Lyman: We elect these people. And not for nothing, but if we'd been the world's policeman in the thirties, you and I...
Toby Ziegler: We'd have had a lot more relatives.
In the previous two examples, the sentence structure was
"Not for nothing" <verb> <rest of sentence>
but in the last example, the structure is:
"Not for nothing", <but>, <full sentence>
I suspect that the phrase is being used idiomatically in the last example, but I am unsure of the meaning in this context.