Are extra unused columns helpful in future?

Currently, while creating tables, we create 4 to 5 extra columns with temp names like c0, c1, c2 etc. to be used later when needed and are left NULL by default. This way we don't have to create additional columns when needed. We just rename one of the temp columns created in the first place. I am wondering if this approach is good or not. Also, what is the performance difference if new columns are created vs renaming old columns.