Question

is there any reason (safety?) why someone should rename the ASP.NET Session Cookie Name or is it just a senseless option of ASP.NET?

Answer 1

If you have several applications running under the same domain on the same server, you may well want to have seperate session cookie names for each one, so that they aren’t sharing the same session state or worse still overwriting each other.

See also the notes for the Forms Auth cookie name:

Specifies the HTTP cookie to use for authentication. If multiple applications are running on a single server and each application requires a unique cookie, you must configure the cookie name in each Web.config file for each application.