A lot of inventors have heard about provisional patent applications, and very often inventors come into my office saying that's what they need. Provisional patent applications can be useful and effective, but, like everything in the law, it just depends.
A provisional patent application provides the applicant one year of patent pending status. Provisional patent applications are never examined, and before the expiration of that year, a utility patent application must be filed in order to claim priority to the provisional patent application. Otherwise, priority will be lost. In some cases, patentability is lost if a utility is not filed before the one year anniversary of the provisional patent application, but it depends on some other factors, such as public disclosure dates.
Provisional patent applications are attractive because they typically require less work than a utility patent application, making them cheaper if you're hiring an attorney. The requirements are less stringent for provisional patent applications when compared to a utility patent application, and can typically be prepared in a much shorter period of time. It allows for an inventor to get something filed relatively quickly in order to secure the priority date. That is especially important now that the US is a first-to-file system (we were previously a first-to-invent system).
Caution does need to be taken when filing a provisional patent application. Oftentimes, an extremely barebones provisional patent application is filed. This can result in issues down the road. The provisional patent application must be enabling, meaning that it enables one with ordinary skill in the art to re-create the invention. If a utility is filed claiming priority back to the provisional, and it is determined that the provisional patent application is not enabling or does not properly describe the claimed invention, the original priority date may be lost (and potentially patentability depending on public disclosure dates). It's easy to see the potential issues in that situation if there is ever a lawsuit, such as one dealing with patent infringement.
Don't skimp on the provisional patent application. Spending a little more time and money on the front-end will not only better-ensure that there are no issues later on dealing with enablement or disclosure, it may very well decrease costs on the utility patent application. There's no need to reinvent the wheel, so a well-drafted and researched provisional patent application can be used as a nice starting point when drafting the utility patent application.