Apple's servers
perform the speech recognition for you. If you use Enhanced Dictation, your Mac will
convert what you say into text without sending your dictated speech to Apple ... turn off both Sin and Dictation, or switch from using server-based
Dictation to Enhanced Dictation, Apple will delete your User Data, as well as your recent
voice input data
https://www.justice.gov/epstein/files/DataSet%209/EFTA00289184.pdf