There are quite a few hosting out there that offers high-limit or unlimited amounts of disk and/or other resources, such as bandwidth transfer, email or FTP accounts. The intention of those web hosting company is to provide ample resources for customer convenience, so that customers needn’t to worry about exceeding limits.
However, users must understand that these resources are limited by physical restraints of technology as well as by reasonable limits of a shared resource environment, especially on shared hosting account.
So, user should know that single account is entitled to utilize the server resources, within reason, up to what is allotted or by what is physically available.
If resources become scarce, host provider will reserves the right to limit users of the affected machine to a lower limit to preserve the effectiveness of the service for all users. If a particular user is in extreme excess of what the average users of the machine have in use (actually used) of their resource allotments, that customer may be asked to remove content, cut resource usage, or relocate to a dedicated service provider.
This is limitation of those so called unlimited space/bandwidth. Make sure you always read and understand their term of service before you signup.