This is going to be an After Effects 101 question, but I don't know how to google it, so here goes. What is the difference between dragging something from your Project directly into your timeline and dragging it into the New Composition button first? Know what I mean? What's the difference between creating a composition out of something and just dragging it directly into the timeline? You CAN do that, so what difference does it ma me if you turn it into a composition first?
If I correctly understand the question, dragging an item from your project to the New Comp button will create a comp with the attributes of that item. Dragging an item to a timeline will merely add it to the composition while maintaining it's original attributes.