Any explanation or benefit?

schema_migrations table is a part of the data that should be dumped to structure.sql. If you look at the original task that is not patched in rails source code you will see that activerecord/lib/active_record/railties/databases.rake includes the following lines of code in the structure:dump rake task:

  if ActiveRecord::Base.connection.supports_migrations?
    File.open(filename, "a") { |f| f << ActiveRecord::Base.connection.dump_schema_information }
  end

This is done so that when rake db:reset is run you would be able to do rake db:migrate without any failures