What are Focus Sessions?
A Focus Session is a set of tabs you save from the Chrome extension. Markwise titles and summarizes the session so you can pick the work back up later.
They are not login sessions. From the extension, save the window (⌥⇧S). Markwise stores the tab set, generates a title and summary, and you restore it later instead of leaving 23 tabs open.
The tab overload calculator estimates the cost of not doing that.