A reseller account allows you to resell full access to your client's space including the Cpanel.
Most of the offline businesses I plan on dealing with will have no idea what a CPanel is or what to do with it. I will most likely be creating a website for them using Wordpress then hand over the keys (username and password). I'll also show them how to update it on their own.
So, is there any reason why I should pay more per month for a reseller account when I can simply use an Add-On domain with my account for free? (Actually I pay $9.95/mo for all the unlimited stuff).
Once I give them the username and password for their Wordpress account, I don't think there would be any reason for them to use the Cpanel, would there?