OS X Dictation - more accurate transcription
Generally speaking this info is sent so it recognizes people and places. I would also imagine that it will use address information to infer what you are talking about and make more accurate guesses.

Apple has a rather long, informative, article on dictation here:

https://support.apple.com/en-us/HT202584

And has a way to change it to Mac-Based dictation so your info is not sent to Apple.