Copying Thunderbird profile to new computer while continuing to use old computer

In the [[Move Thunderbird data to a new computer|Move Thunderbird data to a new computer]] article, it says under "An alternative method for Mac": "CAUTION: Do not open Thunderbird again on the original computer - unless you repeat the process in reverse to transfer the folder contents back to the original computer before opening the app. (If you forget, you can manually check one version against the other to ensure important messages are retained, but it's messy and time consuming.)" It's not entirely clear to me why this would be an issue, but it makes me wonder if that would make the following use case problematic: # The user already has Thunderbird on "Computer A" set up, and wants to copy their Thunderbird profile onto "Computer B" to get the same setup and email accounts on both computers. They intend on using both "Computer A" and "Computer B" simultaneously. ''For simplicity's sake, let's assume all email accounts use IMAP, so emails are synced with the server, and thus simultaneous access between multiple clients is possible.'' # The user follows the instructions to copy their Thunderbird profile from "Computer A" to "Computer B". # The user opens Thunderbird on "Computer B" to make sure everything is working (let's say it's working and emails are syncing to "Computer B"). # The user then opens Thunderbird on "Computer A". Their expectation would be that they would see the same emails and settings as on "Computer B". If they composed/moved/deleted an email on either computer, those changes would sync and be visible on the other computer. Would this be an issue? Or should the user just start anew on "Computer B" and manually sign in to all of their email accounts again?