The reseller package you select offers you a set amount of disk space and bandwidth you can divvy up and resell as you would like.
Please note: this is not the same as reselling a basic HostPapa shared web-hosting plan; reselling a HostPapa shared plan is not permitted.
Most sites do not need or use unlimited disk space. You can create the size limits and feature set you would like to pass along to your customers.
There is a technical reason for the apparent difference in space: each shared plan has only one primary user adding content. Because reseller plans involve a number of users – each creating and saving files and folders – more resources are used. The system overhead is higher; this is why the reseller program is priced differently.