WHY?
By allowing students to interact with technology in an creative manner, other than power point, students can now show their work, tell a story and illustrate it as well as provide additional impact on what it meant to them by voice fluctuation. Another benefit of screencasting is allowing for students to have a "Voice" in the content, process, and product. Thus, making such an project more student centered than teacher centered.
In all, screencasting can provide students the ability to allow for viewers to understand their thought process and paint a mental picture of their demonstration. Another benefit is that students develop a deeper understanding of the material as the screencast serves as a way for them to teach others.