This feature is most useful when you have a large team working on a particular database. Context-sensitive help means that the chief editor can add instructional messages to each data field. This way, the editors can see directly what kind of information they are supposed to enter.
Say for example, you have a collection of pictures and would like to add a data field “Location”, to specify where the picture was taken. What you certainly want to avoid is that each editor chooses the format he or she prefers, because it might lead to a variety of different entries:
Paris in France
This would result in completely inconsistent data. To avoid this, your instruction might then be: Please enter location like this: City, Country; as in: Paris, France.
For getting the most consistent data entries, you should also consider setting up a controlled vocabulary for that field.