I work quite often with EXCEL and what is quite annoying is that when you double click on a file, EXCEL will open that file in same program instance. In that case, you will not be able to see these two files on different screens (if you are using two screens) or simply to compare them next to each other. Following button will open excel file in new instance of the program. Just select EXCEL file (not double click) and then press the button:
"C:\Program Files (x86)\Microsoft Office\Office14\Excel.exe" {filepath$}
Please note that path to your EXCEL installation can be different.
Simon