There are two kind of icons (except good and bad ones):
a)You can use it or recoloured versions for various things, elements, spells, ist may be an ability or an attack icon, an upgrade or an item (for example this, air sphere,etc).
b)You can use it for only one or even a very few applications. I prefer the first kind of icons, but my icons mostly belong to the b) part.
http://www.hiveworkshop.com/forums/resource.php?t=104799#post885333