Advantages of Designing Sub-Patents based on an initial wide-ranging Patent owned by the same inventor?

Question

As a general rule of thumb, what would be the main approach/advantages to designing a series of secondary patents, all based on a broad initial patent, but which are themselves more specific to certain use-cases/industries over having a long claims list in the initial patent? This, while the initial and subsequent patents being owned by the same inventor(s)?

An example : an inventor is granted a Patent over a process of making a wheel turn. He/she then files two more patents, both of which utilize that same process, but where one describes a method for generating electricity instead of turning a wheel, and the second describes a method for powering a saw mill (to cut timber).

Why submit these two extra patents over submitting just the initial one with these use-cases as claims?

If this approach is more advantageous, how would an inventor refer to the initial patent without re-writing everything?

Context: Basing this on a real-life case I'm studying concerning sports tracking equipment.

Answer 1

It is often better to include everything in a single specification and then file different claim sets in different patents sharing the common specification. The downside is that if you sell the patent, typically the buyer requires that you sell them all patents in a given patent family.

Now that the US is using a first-inventor-to-file system, which all of the other major economies were already using, you need to be very careful that your own patent filings, once published, don't render obvious subsequent filings.

Imagine this sequence:

1/1/2016: File first patent wheel turning 7/1/2017: First patent gets published 8/1/2017: File second patent generating power from turning wheel

The examiner could then cite the published first patent application as rendering obvious the second application. It is well known that a turning wheel may be used to generate power. The other issue is that somebody else may publish a thing rendering the second patent obvious between filing the first and second application.

There are solutions when you come up with new material later, but they also have a downside. For example, there is a continuation in part, which allows you to get the benefit of the first patent's filing date for stuff enabled in the first filing and then you get the actual continuation in part filing date for stuff enabled in the second filing. You can mix and match. The expiration of the patent will go back to the 20 years from filing the first application, though.

Overall, this is a complex question where the answers vary based on how you intend to dispose of the patent (if you're selling it, separate filings may be preferred). Best to see a patent lawyer to get the answers.