If you manage a system that's accessed by multiple users, you might have a user who hogs the disk space. Using disk quotas you can limit the amount of space available to each user. It's fairly easy to set up quotas, and once you are done you will be able to control the number of inodes and blocks owned by any user or group.
Control over the disk blocks means that you can specify exactly how many bytes of disk space are available to a user or group. Since inodes store information about files, by limiting the number of inodes, you can limit the number of files users can create.