In SQL Server, what is the purpose of grouping stored procedures?
This is like overloading a method. Essentially you could create two or more versions of your stored procedure, where each does different things - take a different number of parameters, operate on different tables, have different output, etc.

They are called Numbered Procedures and they are absolutely deprecated (announced since 2005). They are still supported in SQL Server 2012, but some features don't play nicely with them. For example, they are considered a containment breach in Contained Databases, and any procedure numbered > 1 will not be created:


  Msg 12829, Level 16, State 1, Procedure blat, Line 1
  The stored procedure 'dbo.blat' refers to a group of numbered stored procedures. Numbered stored procedures are not available in contained databases. Please consult the Books Online topic Understanding Contained Databases for more information on contained databases.