Hi Panos I always use photobucket.
If I understand your question correctly I would say that is because when working on photobucket you are working on temporary copy of the original photo. So the program gives you the chance to save copies or replace the original.
One warning, when you replace original there is no "undo" command. So be carefull with that.
I never do copies btw because I upload copies and keep the original in other folder.
Photobucket is really good. The options to edit the pics are great, I enjoy it every time!