Rigging line should have some stretch (dynamic rope) while tree climbing line is static (doesn't stretch). The point is that when you drop a piece while rigging it doesn't shock load the system so much. Just an FYI: Rock climbing rope is dynamic. Rock climbers expect to fall several feet, so they want some "bungee" effect. Tree climbers should not be taking big falls so we use static rope. Static rope is easier to climb with because all of your energy goes into pulling yourself up rather than stretching the rope. (Again...different for rock climbers because they are climbing the rock, not the rope, so it doesn't bother them to have that stretch).