There are two main reasons why inventors choose to re-file their provisional patent application:
- They simply do not have enough money to pay for the full utility (non-provisional) application which usually costs at least $3,500 including attorney/agent time
- They are still working on their invention and are not ready to commit or be locked into a specific design (once we file a patent application you cannot change it or add any "new matter" to that application).
Although many patent attorneys cringe at the idea of re-filing a provisional patent application as there are some major drawbacks to this approach (see warnings below), I believe both of these are legitimate reasons for at least considering this strategy. Just a few days ago I was speaking with an inventor who simply did not have any money and could not even afford to pay the filing fee for the non-provisional application (about $430 in her case). She was still excited about her idea and had not yet shown it to anyone (this is important - see warning below). In her case her options were to either (1) let her provisional application expire and not pursue a patent or (2) take her chances by re-filing the provisional application which only cost her $70 and bought here 12 more months to raise money. In a perfect world where everyone has plenty of money to spend on patents I would agree with my old-school patent attorney mentors that re-filing your provisional is not a good idea and should never happen, however, when you are working with small companies and inventors trying to boot-strap their projects we sometimes have to take the lesser of two evils and come up with alternative strategies to protect their inventions.
*WARNING - Now for the warning I mentioned earlier. The risk of re-filing a provisional patent application again and again is that each time you start with a brand new filing date and you cannot link your provisional applications together. Just think about this for a minute. This means that you are losing all of the benefit of your first application and are starting over again with a new (later) filing date. Most of the time this is okay, however, there are times when your competition may invent an identical or similar device and may be able to "jump ahead of you in line" at the patent office or possible block your patent from being allowed. For example, if you filed your first provisional in March 2013 and it expired in March 2014 (one year later) and your competition invented a similar device in April 2013 and started selling it online at that time, then if we re-filed your new provisional application in June 2014, the the patent office could use your competition's April 2013 invention to block you from getting a patent because your filing date would be seen as June 2014 (i.e. after their invention was introduced). This is rare but I have seen it happen a few times and it is devastating for our inventor to know that they invented something first and even filed their first provisional before their competition but they still could not get a patent approved because of the unfortunate timing.
International Risk: if your idea was made public or offered for sale (either by you or by someone else) prior to you re-filing the provisional, you will lose the option to file in countries outside of the USA because they have more strict rules on "absolute novelty". So if international patents are important to you, this re-filing decision becomes even more serious. However, if someone does not have a few thousand dollars to pay for their US patent its unlikely they will have the $100,000+ it often costs to file in multiple countries and regions so this is unlikely concern.
In summary, re-filing a provisional application is not ideal and if everyone had the funding available for patents it would be very rare that we would ever re-file a provisional application. For the type of inventors I normally work with (small businesses and solo inventors), re-filing a provisional is often the lesser of two evils. It buys our inventors 12 more months to try and raise funds or test their invention but it comes at a cost/risk. The cost/risk is that you are giving up your earlier filing date from your first provisional and hoping that during the past year your competition did not launch their own product or file their own patent which could be used to reject your later re-filed application.