[Plugin: WP Super Cache] Cache expiration

Hi,

I would like to know how exactly works the cache expiration. In the WP Super Cache Options you can set the Expiry Time in seconds, so I suppose that every X seconds the cache files are re-created even if the page content is not changed.
Since I have a lot of posts that will don’t change more (about 500/600), I think that’s more efficient to generate once the cache files and re-create them only if the post content is changed.
Does WP Super Cache works this way? And if not, there’s a way to do this?
Can I safely increase the Expiry Time to a month, six months, one year?

Thanks in advance.