Some platforms are genuinely run more than once by the same person. An agency might operate one MailWizz install per client, or a publisher might run separate Sendy installs. At version 1.0.88, multi account support is built into the MailWizz and Sendy connections.
How it works:
The first set of credentials you enter stays exactly where it always was, and is treated as the primary account. Extra accounts are added on the same connection card, each with its own label and its own credentials, and their lists appear in the bridge builder alongside the primary account's lists.
Why this is safe to turn on:
A list belonging to the primary account is still identified in exactly the same way as before, which means every bridge you have already saved keeps running through the untouched original path. Nothing is migrated and nothing needs re-saving when you add a second account.
How many accounts:
The connection allows a generous number of extra account slots, and the card offers a couple of blank rows at a time so you can keep adding as you need them.
Labelling matters:
Give each extra account a clear label, because the label is what you will see when picking a list in the bridge builder. Client names or install nicknames work better than server hostnames.
What this is not:
This is not a way to connect two accounts of a hosted platform that only supports one API key per connection. Where a platform is not on the multi account list, the connection holds one set of credentials.
AWeber is a related case:
AWeber's two cards are two different connection methods rather than two accounts, so use AWeber Developer OAuth when you need AWeber to work as a source.