Transferring data uses up network bandwidth, the same network bandwidth that all users in your area utilize to access the internet. So if one user in your area utilizes 1000 times the bandwidth that everyone else does, the network may suffer for all. In those cases, it takes additional resources to manage the network to ensure reliable internet access for everyone.
That is why we have to actively manage each network and have a plan in place to provide for additional network resources when needed. By allocating bandwidth based on the service level, we can optimize our resources accordingly.