The main reason is for consistency. Rather than having both the telephone number of a particular line, and a descriptor since not all of my telephone numbers are public – I had just decided to use a descriptor. To help identify the descriptor, I place them in between brackets [ ]. You can then visit the page about that descriptor in the Numbers Section to see what that number’s role is, and if there is a telephone number available to the public. You could also visit the home page of this site to find out all of the available public telephone numbers.
One reason where this method might make sense to the reader is if I changed a telephone number you have acquired from this website. If I changed the one telephone number, I will then have to go through nearly 2 dozen websites to make sure I made the appropriate changes. In this method, I link the descriptor, and the person can go to the appropriate page, and if available, that number will show on that page. This means, I will only have to make the change to the one page.