Online financing applications for vehicles help to make it easier to obtain financing for the car you want. Not all dealerships will have the online application but the ones that do, they are the ones who are going to help you get in and out rather quickly.
A good dealer is going to help you as much as they can to get you into a vehicle. If the dealer thinks that you will not qualify for financing, they would rather tell you up front rather than spend all the time trying to get you a car and filling out the paperwork to see if you are approved or not. The time that they spend on you can be spent on someone who is better suited for online financing.
The online financing application will ask you all the important questions that the dealer would have asked you anyways. It will simply cut the amount of time that you would have spent at the dealer when you fill it out at home.