Both lower_level_thinking worksheets and too many (even high quality) worksheets can hold students back by not providing stimulus and challenge. Studies have shown for years (just do a Google search!) that children learn best through active involvement and real_life experiences. Virtually every teacher knows that children learn to read by being exposed to books and by being read to, NOT by completing worksheets. The same applies to all areas of learning.
After you create the group, the word "group" appears in the title bar of the workbook. Once they are grouped you can format one worksheet and all of the worksheets will have the same formatting. You can insert a row in a worksheet and the same row will be inserted into all worksheets. This is a great tool when you need for all of your worksheets to have the same formatting.