I have partially migrated some documents from my 2011 I-Mac to my new MacBook Pro using the Migration Assistant. A curious thing happened in that I now have two separate accounts on the MBP, with different passwords quite unintentionally. One is from the I-Mac, the other from the initial settings of the MBP. It was a little alarming at first since the usual MBP password & fingerprint would not work, and of course, a great deal more storage space is now occupied. I intend to make use of the new arrangement and keep the two accounts. Yet to be seen whether Time Machine backups of both are made.