In the second step of the car buying guide you'll want to arrange your own financing and get pre-approved for an auto loan. Of course, you could let the dealer arrange this for you, but you'd probably change your mind after reading about car dealer finance profits and how much they make arranging loans.
Outside of the profits the dealer makes from arranging financing, having a blank check in your hand from your own source allows you to buy like a cash buyer. It simplifies the negotiation process and helps you focus on the only number that really matters, the sales price