.inc extension , why to use it ?!

What is the benefit of making some files with extension " .inc or .ini " in a PHP script ???

i found this line in website introducing php tutorials ,

 
include "connect.ini";

in the file " connect.ini " they put the code to connect to Database …

I tried on localhost to do this , it worked fine … but i noticed a big problem …

when i request the file .ini from the browser direclty , it is downloaded !
and when i request the file .inc from the browser directly , its code is shown on the screen …

so , what is the benefit of using them , and when and why to use them ???