you dont
need it to apply to those positions, but id say it would look good on a resume/contribute to an application (saying you got leadership skills/participated in stuff at mac) .. but if you dont go thatd still be fine, you have tons of other opportunities to participate in things at mac that would give you leadership skills (like clubs, IRC, etc)
...horizons was an awesome experience though
i would suggest doing it because it was so much fun and kinda gave you a headstart on the whole mac/university experience