iTunes - Manually Manage Music Will Not Stay On, Why?

[iMore Question]

iTunes - Manually Manage Music Will Not Stay On

Hello,

I am using latest version of iTunes, and am on a PC.
I keep checking "Manually manage music" and when I come back to iTunes it is not checked.

1. Any ideas?
2. What is manage music manually exactly doing?
(I mean it does not seem to affect anything. I move my music around with ease no matter what).

Thank you.