Kitty:
If you're going to use gerunds, it's wise to stick with
action verbs. I could never imagine looking in an Index for
conceptual ideas like "Understanding," "Viewing," "Advanced
Features," etc.
You might know what topics are advanced, but how could your
user possibly know that? I would stick with "Fringe Benefits" and
"Benefits," and the common "Adding," "Deleting," etc. Otherwise,
keep it to nouns, nouns, nouns, such as "Vacation Days," "Sick
Days," "Bereavement," etc.
Also make sure you present index entries for the titles of
every window and panel in the application. There's nothing more
frustrating to me than not finding such entries.
Good luck,
Leon