What is the difference between Add and Add(BCC)?

[ElectriKong]

I have been wondering what the difference is.
In case you don't know, these are how you add recipients to your PMs.

[Shadow Yoshi]

When you add someone to the "To" field, they'll receive your message and will see who else it was sent to. If you add them to the "BCC" field, they'll receive your message but will not see anyone else it was sent to.