Adds a note to further clarify, what's the effect of this setting

Author: koskila

sharepoint/sharepoint-ps/sharepoint-online/Set-SPOTenant.md

@@ -301,6 +301,9 @@ The valid values are:
 False (default) - When a document is shared with an external user, [email protected], it can be accepted by any user with access to the invitation link in the original e-mail.  
 True - User must accept this invitation with [email protected].
 
+> [!NOTE] 
+> If this functionality is turned off (value is False), it is possible for the external/guest users you invite to your Azure AD, to log in using their personal, non-work accounts either on purpose, or by accident (they might have a pre-existing, signed in session already active in the browser window they use to accept your invitation). 
+
 > [!NOTE] 
 > Even though setting the value is instant (if you first run **Set-SPOTenant -RequireAcceptingAccountMatchInvitedAccount $True**, and then **Get-SPOTenant -RequireAcceptingAccountMatchInvitedAccount**, True should be returned), the functionality isn't turned on immediately. It may take up to 24 hours to take effect.