When I operated a small personal site sometime back, I didnt really care/look much into the tons of available features.

What are the most useful features for a site owner? Is any specific feature especially useful for a certain purpose?

The reason i chose to use cpanel with my hosting company. Is mainly, because it is the most popular and most people know how to use it. It is also very easy to navigate round in my opinnion.

It's easy to use, popular, the majority of people prefer it, it has more addons and extras than any other panel. It has most features on it, incorporates with the billing system very nicely and makes sales automated - making our jobs a lot easier . I cannot comment about which is the best as i found every feauture in cpanel is great but i like the fantastico scripts the most .

I love Cpanel in fact I tried at one point to use another program but found myself calling up the company to cancel because I could not figure out how to use the others.

As far as good stuff there are forums and chat rooms and autoresponders and databases. Lots of useful things it really depends on what you are planning on doing with your website. Hope this helps!