A lot of hosts started as resellers.....including HostRocket.
A reseller packages allows you to get your feet wet without spending too much time or effort troubleshooting servers issues, etc.
In addition, ANY business should try to keep costs as low as possible, in order to maximize profits....a reseller account allows you to do that.
Once you have built your revenue stream to where you can afford a server of your own, and still live comfortable, then only then should you jump for a dedicated server.
Of course, if you have the capital to go with a dedicated server from the beginning, then you should go dedicated right away. Another alternative is to set that capital aside, go with a reseller plan, and then once your own revenue is built, etc go with a dedicated server, and either use that capital in other aveneues of your business, or simply give it back to the investor (if it was a loan)