Why use new?

In the below code I make 2 instances of the class Bob. The first 
instance does not use new (automatic allocation?) and the second 
instance is used with new (dynamic allocation?)


#include<iostream>

class Bob {
	public:
		Bob(int a): n(a) {}
		
		int getn() {
			return n;
		}
		
	private:
		int n;

};

int main() {
	Bob b1(22);
	printf("n = %d\n", b1.getn());
	
	Bob* b2 = new Bob(88);
	printf("n = %d\n", b2->getn());
	
	return 0;
}


But when are there any reason to use new?

And will the b2 pointer automatically be deallocated when main returns?