Apart from being non persistent and scoped only to the current window, are there any benefits (performance, data access, etc) to Session Storage over Local Storage?
Few other points which might be helpful to understand differences between local and session storage
Both local storage and session storage are scoped to document origin, so
https://mydomain.com/
http://mydomain.com/
https://mydomain.com:8080/
All of the above URL's will not share the same storage. (Notice path of the web page does not affect the web storage)
Session storage is different even for the document with same origin policy open in different tabs, so same web page open in two different tabs cannot share the same session storage.
Both local and session storage are also scoped by browser vendors. So storage data saved by IE cannot be read by Chrome or FF.
Hope this helps.