Microsoft's docs for "Hosted Email (Exchange Online)" say that a connected account is checked for new email once per hour. "If you want more immediate receipt of email, configure that account to forward mail to your Office 365 account." But it either says or implies that the outside account should be "Connected" AND be forwarded.
If you've configured an outside email account to forward to your Office 365 account, what is the benefit of having it connected, too?