In some cases, our server will run out of disk space. Sometimes it will take time for us to migrate to a bigger node and or extend the disk. 

It would be faster to allow website files to be stored on the new or extended drive. 

For Example. 100 Website is located on 1st Disk. Then, when it full 101st and other additional website will be hosted on 2nd drive and so on. With this, as an admin will save our time more than migrate our entire server to a new bigger server.