What is the use of TABLE maintenance generator?
Table Maintenance is used to maintain the values of a custom table. Based on the requirements, one can change or add/delete the contents of the custom table.
Table Maintenance generator (TMG) is required to do Manual entries in the Table. If the requirement is to update the table only programmatically and not manually then table maintenance generator is not required.
Manual entries in table can be maintained (New record can be inserted / existing can be modified) using transaction SM 30, if the table maintenance for the table is generated.