This saves having to remember to do STRING(TOUPPER) in every cmake file.
At times that's really not convenient if possible at all.
For example when a top-level project is guessing what option some
subproject is going to use and tries to use it for the builtin options
view. The acutal OPTION statement is not there, and it's not nice to put
a string(toupper) on a variable that seems to come from nowhere (and in
fact it might not be there at all).
