What exactly does 'using the same profile for both' mean?

To me (not very knowledgeable about these terms0 it means that the settings and messages and address book are identical The desktop is up stairs and the laptop down and I use whichever is handiest. I know that if I just delete content from Thunderbird on either it will have effect on both - is this right. I am guessing that if I format my laptop hard drive it will not affect my laptop Thunderbird. Glad of any help. arnold s. (a.green)

I know that if I just delete content from Thunderbird on either it will have effect on both - is this right.

Assuming your account is set up as IMAP on both computers, then this is the way it works. Changes you make while Thunderbird is running are propagated to the server, and then synced to all other clients.

Wiping the laptop will not have any effect on the desktop Thunderbird, no changes are propagated to the server in that case. Wiping in my understanding is you boot the laptop from a CD/DVD or USB stick, and use some sort of wiping software to override the entire disk.

In any case, create a backup of your Thunderbird profile on the laptop prior to wiping it, just in case. http://kb.mozillazine.org/Thunderbird_:_FAQs_:_Backing_Up_and_Restoring