Not to answer for Caroline, but I would imagine it is to keep the threads intact, even if people's photobucket accounts change. It's to avoid having a thread full of little red x's in a year.
Also, (recap of something Carlos made me aware of and a pretty cool feature), if you upload photos and their names appear at the bottom of your "New Post" window, you can mouse over those links and see what number they have been assigned.
If you take that number (just the number) and place it in attach tags like so...
[attach ]628[/attach]
(without any spaces)
You image will appear where ever you paste that code. So you can place your attached images anywhere in your post that you choose.
