I mean, afaik the standout feature of Picasa was shared web albums where you could invite people to add photos and permissions were managed via Google accounts, so, it's easy to confuse the two. From memory the only thing that changed when moving from Picasa to Photos was that I no longer had a desktop app where to keep photos on disk + Picasa had a neat map of geolocations (maybe Photos caught up or can you still not view photos on a map? I know apple does this, I just use ACDSee now and keep it offline)

Sunsetting blog from 2016 for good measure: http://googlephotos.blogspot.com/2016/02/moving-on-from-pica...