>Actually I didn't ask about Web server. I did install all the components of IIS and enabled it on my Windows 10 PC. It works well.
>There is an option for FTP Server in Windows 10 Features. And this is what I was asking about.
>I didn't choose it and so far don't need it. I am sure if I ever need it, it is a simple step to enable it.

IIServer main part was the Web server. Rebranded IIServices offer HTTP(S), FTP(S) and additional services.
If you don't need the Web server, what is the specific need to install IIS ?
If you need the Web server, it can do the things FTP server offers (file transfer to/from other machine) for machines running without Webserver in DMZ, but under another protocol and without the tools/functions typically used for file transfer.

A FTP server in DMZ is standard for those companies trying to minimize attack points on a given machine but need file transfer, which a web server offers in-built as well, but via other API/Protocol.

You are asking "do I need to buy a green reserve gasoline canister?" without telling if you drive a Tesla or normal car and you don't even tell if you have a gasoline station on your property or if the car is driven outside your property ;-)