Be careful when using groups because if you forget that your spreadsheets are grouped and then proceed to add or change figures on a worksheet, all of the worksheets in the group will have the same figures. To remove a group, simply click on a sheet that is not in a group. If all of the worksheets are grouped, right_click on any tab and choose Ungroup Sheets. Keep an eye on the title bar prior to making changes and Excel will tell you if the sheets are grouped.
You can use the Fill command in the Editing Group on the Home ribbon bar to fill information across worksheets when they are grouped. For example, if you add a few worksheets to your workbook and you can to copy parts of one worksheet to another, you could use copy and paste, however, this could take several operations to perform. By grouping the worksheets and using the fill command, you could quickly copy parts of the original worksheet to the new worksheets inserted into the workbook.