Remove synced mailbox for migration

Hi Guys,

Is it really not safe removing a mailbox that already "synced" for migration to the cloud? It's an option available, but I read the article below and made me hesitant. 

https://answers.microsoft.com/en-us/msoffice/forum/all/deleting-synced-migration/1a95a621-2e66-4472-968f-5d4b10518196

Thanks!
Uddan