A provisional patent application is limited term application that preserves the priority date or filing date of your invention for further applications. It is usually the starting point of most inventions.
This application last up to 12 months and is international recognised. It gives the inventor standing to further applications overseas and backdate the application to the original filing date.
One of the key drivers for using this type of application is that delays the costs of filing overseas by at least 12 months. The inventor is not forced to pay any more for the application.
Another advantage is that you can join one or more provisional applications into a single application at a later stage. This essentially means as your invention improves along with your knowledge. You may be able to file additional provisional patent applications for the incremental improvements.
A final advantage is that it delays making a decision as to which countries to pursue patent protection in.