One advantage to a provisional patent application is that you can file more than one during the 365 day period as you come up with further modifications and improvements to your invention. These provisional applications can then be filed in one overriding nonprovisional application at the end of the 365 day period from when the first provisional patent application was filed. Since provisional patent applications cost about 20% of the cost of a non-provisional patent application, you can see that this might result in a significant cost saving. This can also work just the opposite way, where you file a single very complete and detailed provisional patent application containing a multitude of inventions, for a single fee of (currently as of January 2012) $125. I have done this several times for large companies because they know what they are doing and know the risks and the procedures needed to avoid those risks and this allows them to protect the filing date on a multitude of inventions at negligible cost in government fees. When the end of the one-year term of the provisional patent application comes, the company then files provisional applications for those inventions it wants to pursue. I had one case a couple of years back where a major company filed 17 non-provisional patent applications claiming the benefit of a single provisional patent application I wrote. Another procedure, which I actually think is better strategically would have been to file 17 identical provisionals and then file up to 17 non-provisionals based on those, and just reference the ones you want made public in each of this 17 non-provisional patent applications. That way any opponent in a patent infringement case cannot get into the files of the other 16 applications to try to discover invalidity arguments based on the file histories of those 16 other cases. Now, that is way over the head of most inventors and so the point of all this is to show that in inventor has no business doing this without a registered patent attorney guiding the way, as it is fraught with peril and these patents can be worth millions of dollars in the right situation, and as you can see from the above their are many options for the skilled patent attorney to pursue depending on what is best for the client in a particular situation.