500 MS Rewards points available for an achievement in this. Maybe that's why you started, but wanted to make sure you know.
Thanks, that's why!
GTA Online: Complete all 10 waves of a Survival. - Grand Theft Auto V
GTA Online: Kill the thief that mugged you. - Grand Theft Auto V
GTA Online: Call for a Backup Helicopter for the first time. - Grand Theft Auto V