Why do many transactions have no attachments?

I’m trying to restore some tickets which were removed from version 4.4.4 prior to upgrade to 5.0.3. I have noticed that many transactions exist without attachments. Is there any reason I should reinstate those transactions?

A transaction in RT can be more than just an emailed reply or a comment being added, so yes, you probably need to reinstate them if you want the ticket history to be correct.