mu-cfind is meant to search for contacts within your contacts database and the emails that you have sent/received. The use of the --personal flag in that command is meant to filter for only emails that use your email addresses (which are all the ones you specify with the ${myAddresses} variable. Disregard what I said in #1623 (comment).
--my-address=<my-email-address>
specifies that some e-mail addresses are 'my-address' (--my-address can be used multiple times).
This is used by mu cfind -- any e-mail address found in the address fields of a message which also
has <my-email-address> in one of its address fields is considered a personal e-mail address. This
allows you, for example, to filter out (mu cfind --personal) addresses which were merely seen in
mailing list messages.
To initialize the database with mu init, the ${myAddresses} is not required to be passed to successfully initialize the database, but it is heavily recommended to do so.
To see the difference, in a safe location, run mu init --maildir=<path>, then mu index. You'll notice that "personal addresses" returns <none>, although the database will still work. However, mu cfind --personal will fail (as the personal contacts don't exist). Then run mu init --maildir=<path> --my-address=<address>, then mu index. Then you'll be able to search for contacts using mu cfind --personal.
