What is the purpose of taping the leading edge of a foam plane? Protection? or aerodynamics?

Protection.

It protects them from hitting rough grass or even debris. I don't do it, but it won't hurt to use some. Don't use heavy duct tape though, duh. I grass land my corsair and don't have any problems, but its nice grass where I fly.

thanks i thought so as i flew my t28 through a tree, it kept going but had a small nick in the leading edge, i also hit a goal post on a dead stick landing and didn't even hurt the plane, I love this durable little plane!