Short story you actually own very few of your days off. Doesn’t mean you’ll get burned every month, but there is the potential for your schedule to get blown up on you, which can make it hard to schedule other activities- especially with a commute thrown on top of it. Some don’t have many family or other obligations & don’t mind the lack of scheduling security, but if that’s not you, NB will give you better control over your reserve schedule, & a quicker path to holding a line.