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.
As far as using worksheets for busy work, the verdict is in. It is destructive to classroom learning to assign worksheets to simply keep students occupied. Busy work creates monotony, causes boredom and increases the likelihood of behavior problems. To know if you are on the right track with worksheets in your classroom, answer (honestly) these simple questions: Do my students groan when I hand out a worksheet? (The answer should be no.) Are my lesson plans based on worksheets? (The answer should be no.) Do I feel anxiety if I don't have worksheets copied? (The answer should be no.) Are students excited about learning in my classroom? (The answer should be yes!).