It is essentially the same thing, with two small differences:
1) One is at the time of installing, the other at a subsequent time
2) In the first case, you do not have to create an account, and can have only the accounts that are transferring; otherwise, you need first to create one (admin) account, login, and then (or later) run Migration Assistant.
You should also take into consideration that this new account you create should not have a name that conflicts with the ones you want to migrate.
For example, say you have a TM backup of your old mac and are starting a new mac you just bought.
Your old mac had two accounts, say "me" and "wife".
You can start your new mac, choose to transfer "from another mac, disk or time machine backup", and have the two accounts ready to use, with all the photos, mail, settings....
You can start your new mac, choose not to transfer anything: you will have to create an account, ...
and then later, if you like, use Migration Assistant to bring back the stuff from your old mac.