Using the NOEXPAND hint can result in an error:
Msg 8171, Level 16, State 2, Line 1
Hint 'noexpand' on object 'dbo.ervStats' is invalid.
That behavior can cause problems and I would expect a Warning to be raised, not an error since the problem does not affect the result of the query at all.
OLTP application using one or more indexed view to speed up some functionalities. This can happen as some db are OLTP but also used for real time reporting that can't be done on a mirror. At some point you may find out 1 indexed view is the cause of excessive locking for 1 specific site, so you remove the index....but must now recompile and redeploy the application to hundreds of desktops to remove that 8171 error message.
If a warning was issued instead of an error, the problem would not occur. Nothing is changed at the LOGICAL level and the query would run as expected is the hint was ignored.
Some concept would hold true for other hints (index hint on a dropped indexed for example).