The program does not leave unnecessary files on your computer.
For those who are interested in Picasa:
The program makes one file in each photo folder, after you edit the first
photo file. The file name will be picasa.ini and it can be viewed if the
folder option is set to view hidden file. You can open it and see how Picasa
is saving your edited changes.
The nice thing about this added file (extremely small size) is that it
contains all the changes made to all the photos in the folder. Picasa does
NOT change original files as you edit them, it only codes the changes made
for each photo and stores the changes in the picasa.ini file. So when
original photo files are opened with Picasa (after editing with Picasa), the
edited photos are seen with all the editing and because everything is coded
every change made can be undone, one by one.
This is great for printing at home. After the editing is done, just print.
No need to save the edited file because when you open it again in Picasa you
get the edited file back. A lot easier than having to save edited files. And
if you want to save the edited file you can, hit save copy and the edited
file is added to the folder, same name as the original file, with 1 added at
the end. All done automatically.