Your brake level is just as important as your throttle!!! It's a marriage and once you get use to using the brake and throttle with each other, your riding will improve!!
One analogy is to think of the brake level like a clutch. When you take go to take off, hold the brake, increase throttle and "feel" for all the slack in the drive train to come out and release the brake and continue to increase the throttle. Same with getting up and on top of deep snow, only much quicker.
When side hilling or tree riding the brake will assist with keeping overall momentum up, without coming completely out of the throttle. If the sled feels like it's getting ahead of you, burn a little brake. If you feel like "you" are getting behind the sled, add some throttle.
Running with a finger on the throttle and learning to use it will increase your riding capabilities. The old school of thought was "when it doubt, throttle out" but really it is "when in doubt, finesse it out" and you need the brake to do that!!