New Google Algorithm Change - Https As A Ranking Signal

“After months of speculation, Google announced that they would be giving preference to secure sites, and that adding encryption would provide a “lightweight” rankings boost. They stressed that this boost would start out small, but implied it might increase if the changed proved to be positive!”

If we change a site to HTTPS for every page, do you need to set up redirects?

You will lose all the rankings in search engines. For now it's not recommended to do that, it's a lightweight ranking factor and for now every SSL page is not indexable because of cs-cart implementation.

And you might want to consider what you gain the the lightweight ranking, you might lose with page speed. Encrypted pages take about double the bandwidth and do not compress as well as non-encrypted pages.