The PPA format is not now, and never was, intended to be a substitute for the NPA. Patents are derived solely from a filed NPA that is examined by a patent examiner and then passes through a prosecution process. There is neither examination nor prosecution for a PPA. The main purpose for the PPA as envisioned by the US Congress was to give inventors, particularly individual inventors or inventors in small companies, a chance to file a quick and cheap application, after which the inventors may seek funding or other business alliances. If the inventors find the necessary funding or other help, they may continue with the much more expensive and time-consuming NPA.
Therefore, although the PPA does allow the earliest possible priority date, it does not shorten the time from application to patent (called “the pendency period”), and in fact it lengthens the pendency period. In the 21st century, the pendency period of US non-provisional applications has been, on average, about 32 months. This has improved gradually over the last few years, from 2013 to 2019, so that the average pendency is about 23 months.1
However, this is solely from filing of the NPA. If a PPA is filed first, and the NPA is therefore delayed for one year, the total average pendency from filing of the PPA to patent issuance would be 12 months + 23 months = 35 months. If receiving a patent quickly is an important objective, then the filing of a PPA before the NPA may be disadvantageous.2
1 On the pendency period, see the US PTO web site at https://www.uspto.gov/corda/dashboards/patents/main.dashxml?CTNAVID=1004, last reviewed on January 15, 2019.
2 There are several ways by which examination a US NPA, and hence grant of a US patent, may be accelerated from the normal pendency period. Some of these ways may cost money, others may not. If time to grant is important, a patent attorney should be consulted.