?? I can't find anything on this specific question!
I don't believe you "HAVE" to -- but it does save a step later. Basically it pulls in whatever you have as your "A" for the A/B test -- think of it like your best bet, or existing champion... then you test against it.
Yes, because you can't approve an email asset without a subject line. You can certainly override whatever the subject line is in the testing part of the email program though.
Retrieving data ...