Rise 360 Icons, GIFs, Vectors vs Stock Photos

I've noticed websites and learning course designers are using gifs and icons more often with less emphasis on stock images.

Is there a best practice for using icons? For example, are they appropriate for corporate training, do you combine icons and stock photos in the same course? Are vector and illustrations considered a modern design for every genre or only used in informal courses?

Thanks for your comments, it means a lot

Terri Rodman - I Design with Rise