To answer this question in full, the end user who might need a reseller would really, really differ.
The main 3 common types of clients are:
1. Those looking purely to push web hosting services (start their own web hosting company).
2. Designers / developers: These people build other peoples / companies websites so it would be a good idea to offer branded hosting for an extra recurring fee.
3. Users with multiple websites: There are several advantages to having a reseller account than mixing them all into 1 single shared account such as organization, flexibility, security and so on.
The main benefits for all 3 would be:
1. Cost: There is no need to buy a server and then all the licenses that is required to make something of it.
2. There is no server management knowledge required nor do you have to hire anyone to manage the server. The web host will take care of all of this for you.