What's the real different or effect of NS1, NS2, NS3...etc??

[eria]

the purpose of nameservers is just to resolve the domain alias and route it to hosting server where it can find data, using multiple dns means to allow mutiple servers or IP's to resolve the alias in case one can't do the job, second will do or vise virsa. but remember resolve domain alias doesnt mean that your site will browse successfully on clients computer, if your hosting server is down then dns can't do anything.
Am I right boys?