Default [Q] Is root password useful?

I have a Kindle Fire HDX and would like to install Google Play Store, do some modifications, etc.

But, I have no experience with rooting devices. I want to know if it's useful to have the root password, because I actually already have it (long story--I know people who can get this information).

However, I have no idea if this is even helpful, since obviously the Fire OS doesn't "ask" you if you have root passw.

If anyone has any suggestions, let me know.