Under Tools-Options-View, there is an option to treat hide zero values.
Also, when dealing with a PivotTable you have the option of making blank
cells display 0.
In math operations, using a blank cell the value is calculated as zero.
However, there is not an option to make all blank cells display zero. (if
you think about it, this would make a giant spreadsheet, making it almost
impossible to print what you actually wanted)