Few years back the installation of operating system is critical task. Its depends upon the floppy disks and compact disks, basis on the lot of commands and capable system configurations. Now a day's its a simple and easy, because the platform provides updating links and even device companies provides recovery disks. But those who not have that stuff, there will be used pirated or commercial compact disk and DVDs. Some times the disks will be not answering in situational conditions. It works upon the CD/DVD ROMs, writers and disk conditions.
Then its a lot of time taken and difficult not user friendly. Used whose tech passionate persons.
So, we have alternative tricks. It is using USB, why not?
Mostly the notebooks and laptops don't have CD/DVD ROMs.