mx or sx

I was looking at some MX and SX photos and I noticed handguards were more prevalent at some races than others (particularly MX). Are handguards only used at tracks with dirt mixtures that include more rocks/hard things?

I'm just wondering if anyone has heard much about who will be where in the AMA MX/SX scene next season. It's been confirmed that Chad Reed will be running his own team with L&M sponsorship, factory support from Yamaha, Nathan Namsey as a second rider and will be managed by Larry Brooks. Brooks...