Templates are a great tool for introducing consistency in certain types of workbooks. An invoice template, for example, can have the formatting and formulas already set up so that the user only has to enter some numbers. It can be a real time saver.
There are two special templates that Excel provides that are worth noting. They go by the names Book.xlt and Sheet.xlt. These templates, when placed in your XLStart folder determine the configuration of normal workbooks and worksheets. If you’re a Word person, they are similar to Normal.dot.
Book.xlt determines the configuration of workbooks that are created using File>New>Workbook. It does not change existing workbooks, only newly added ones. For example: If every time you create a new workbook, you want two sheets in it and you want the first sheet to have extra wide columns and the second sheet to always have the a certain header (in page setup), then you could set up a blank workbook with that configuration and save it in XLStart as Book.xlt. All new workbooks will have this configuration.
Sheet.xlt is the template that determines the configuration for newly added worksheets. It too, does not effect existing worksheets. If you save a one-worksheet workbook as Sheet.xlt (again, in XLStart), then using Insert>Worksheet will add a worksheet based on Sheet.xlt.