SQL Server specific file group
Database schema for all objects is stored in the PRIMARY filegroup although user data may optionally be stored in a different filegroup.  A piecemeal of individual filegroups is not intended to be used to create a new database, but rather to restore critical data before less frequently used data.  That technique allows a database to be partial available for use during a restore sequence before the entire restore is complete.


  if no, what is the purpose of the file groups then ?


In addition to piecemeal restores, user-defined filegroups allow you to control placement of individual tables, indexes, and partitions.  This allows the underlying files to be placed on different underlying storage devices such as in a scenario where isolated storage provides a performance improvement (e.g. segregate random and sequential access) or with tiered storage (e.g. archive data on slower, less expensive media).