Wow you are making things a lot more clear to me now.

can you elaborate on full or diff backup?

If I do it, I will be able to restore to certain point in time again? I guess the point in time restoration allows you to restore to particular time and simple logging will prevent you from doing this and will allow only to restore when the last backup was made, is that right?

How does that command break the log chain? I don't understand that.