1) If you play multiple sports you develop different muscle groups, making you a better athlete.
2) Playing only one sport allows you to focus on the skill sets necessary to become a highly competitive athlete for your sport.
My opinion: Play one sport. Because if you have just one other athlete out there that ONLY plays one sport, guess what, they are your competition! If you want to be the best, you need to be better than that other athlete that is perfecting their/your sport.
Not to mention, you only have your freshman, sophomore, and junior year to make an impression on the coach(s) you will one day play for. If your other sports are taking away valuable time to perfect your primary sport, other sports are actually hurting your scholarship opportunities.
Pick the sport you love and be exceptional!