It means any album changes you make are automatically uploaded/altered online.
You can add new photos, add captions, tweak the colour.
So, what do you think happens if Picasa's database decides to get itself corrupted? The albums still displayed, but the contents had disappeared.
As the albums were set to automatically sync, what do you think happened?
Yup. 90% of the photos I've uploaded over the years have disappeared.
That wouldn't be so bad if I hadn't added the damn things, one by one into blog posts:
If I really want to get things back the way they were, it's going to cost me half a day at least.
Part of me is considering paying for hosting and creating my own site, independently of Google.
The other part is a lazy bastard.
I wonder who will win...