In modern Shinigami society, people that are higher up in rank, will be much more respected than those below. As you advance through the rank, you will get more opportunities, and get more respect off other people. Also generally speaking, if you are higher in rank, you will be stronger. As you increase in rank, your abilities will bloom, and your skills can increase. When you get higher in rank, you will be granted the ability to learn more Kidou. If and when you reach Captain or Vice Captain spot, you will be able to converse with other people of your level, be able to have more say what goes on within the soul society. You can change things, lead your squad to glory. Doesn't that sound good?
There are loads of ways in which you can advance in rank. Firstly, because the amount of Shinigami there are, the new recruits will be high up, and the power distribution between the seats will vary. For example, a seat 2 may be weaker than a seat 5. So once the majority of the seats are filled for one squad, the captain will be forced to do a squad wide tournament, to decide who should go into what seat.
