When to refresh a view

I like to know under what changes in a table will require me to refresh a view that is using that table. For the refresh, I am referring the command, sp_refreshview. For example, if I make a length change of a varchar field from 50 to 255. Do I need to refresh the view? If I add a default to a field, do I need to refresh? etc... Is there an article out there that would show me the prinicple about when to refresh view?
Thank in advance for the help.
wingman

sp_refreshview command is used when you made any changes to the tables.