What's the difference between a 2WD and 4WD off-road RC truck?

2WD trucks like the Slash 2WD XL-5 are lighter, cheaper to maintain, and easier for beginners to control on smoother surfaces, but reviewers consistently note they get hung up in grass and loose dirt. 4WD trucks (Slash 4X4, Maxx Slash, RLAARLO/Amoril platforms) cost more but handle rougher off-road terrain, jumps, and mixed surfaces far better.