If you start with a dedicated server your costs will increase significantly. These funds could instead be spent on marketing or saved for a rainy day. Remember, it is never just the dedicated server that you need to buy, it is licenses for control panel, backup software, backup server, add ons like Cloudlinux and Softaculous etc - And a big one, proper/full server management.
A reseller account has all of these included at a simple $15 - $35 (depending on where you shop) monthly fee. In many cases, it also includes WHMCS for free or another billing software.
And to top the reseller packages off, you have a (normally) 24/7 support team you can reach out to where you wouldn't with a dedicated server unless you outsource / hire employees.