Compression
Compression clickers are very common on sleds these days. This adjustment is made by turning the clicker screw in or out, and position is measured by counting the number of clicks out from all the way in. Compression adjustments change how the shock compresses to absorb impact from bumps, landings and terrain variations. Turning the clicker in makes the shock resist compressing, thus resulting in a stiffer feel which will be more resistant to bottoming out. Turning the clicker out lets the shock compress bumps easier, feeling softer and reaching the bottom of the shaft stroke easier.
Some shocks, like the Fox Float R Evol, have high-speed compression and low-speed compression clickers. The terminology represents the shock shaft movement, not necessarily the speed of the snowmobile. High-speed clicker adjustments will change how the shock absorbs sudden impacts, like square-edged holes, hard icy bumps, firm flat landings, etc. Turning the high-speed clicker in will increase the shock's damping to make the ride firmer and keep the sled riding higher in the bumps (by not letting the shock move as far down on the shaft). Low-speed adjustments are for rolling whoops on trails, transition landings (where the sled lands with the slope) and lifters. Most mountain terrain once off the trail will play into the low-speed adjustment.
It's important to make small adjustments and spend enough time making adjustments so that you can tell a difference. Sometimes a soft compression setting can feel stiff (because the bottom of the stroke will be reached sooner) while sometimes a stiff compression setting can feel soft (because the lack of shaft movement can feel like the shock is bottoming out). Play around with shock adjustment until you can tell a difference.