Initializing NSMutableArray with and without capacity

Possible Duplicate:
NSMutableArray initWithCapacity nuances
Objective-c NSArray init versus initWithCapacity:0

What is the difference between following line of code? what is the exact advantage and disadvantage? suppose next I will do 3 addObject operation.

NSMutableArray *array = [[NSMutableArray alloc] initWithCapacity: 5];
NSMutableArray *array = [[NSMutableArray alloc] init];