If you are hosting large files such as videos, podcasts, or large photo archives is transfer overages. Hosting services often provide a fixed amount of overall transfer with their hosting plans. A plan may include only so many MB of transferred data. After your account has reached that amount, you will be charged for any extra data that is transferred. Depending on the host, this could be as much as $1/MB.
At that rate, a single download of a 20MB file after you’ve reached your limit could cost you $20 extra on your hosting bill!
Usually, the higher the transfer limit, the more costly your hosting plan will be. Some hosting services offer plans with no transfer limitations, which can be quite costly, but certainly less costly than paying for transfer overages on a high-traffic site.