What is the point of DNA sequencing?
No, you don't. Having the DNA in your hand means that you have access to a macromolecule, not more. 

Think of the DNA as a book (or a library). From holding the book in your hands, you don't know what the content is. You have to actively read the book to get this information.

Sequencing a piece of DNA is basically the same. Your readout is the sequence of the bases which is essential to understand (or do research on it) a certain piece of DNA. With this knowledge you can see where genes start and end, define introns and exons (for eukaroytes) and so on.