At work we use to share some Excel workbooks (systems inventories, and things like that). To avoid not being able to open such files because your coworker has already opened it, we always open them in read-only mode. The problem comes when you actually want to make change to the file!
Before we used to close the workbook, and reopen it, this time in read-write mode. Not very efficient, was it?
Recently I found those buttons available in Excel «customize toolbar» options:
* 
«Update File«: With that button, no need to close and reopen to get last changes made by your co-workers ! Just press the button. Like a «refresh-that-file»…
* 
«Toggle read-only«: This button reopen the file in R/W if it was in R/O mode (and the contrary if it was in R/W mode)
I found that buttons very useful. Couldn’t work without them now!
adumont 