@bardencj: 2 thoughts come to mind.
First, yes, if you want to file a complete and lengthy claim set well beyond the 3+20, the amount of fees deferred can be enough to make deferral real savings.
Second, you mentioned a specification that supports broad coverage and I think others have said something similar. It sounds as if that statement is made under the belief that a less detailed specification provides broader claim coverage. That belief is mistaken. Breadth is determined by the claims, not the spec. And, strength of the claims is enhanced by a more detailed spec. Note that "best mode" is included in Section 112, paragraph 1. So, skimping on best mode in a provisional application can render it inadequate.
In fact, following up with the real application a year later requires updating the best mode and can require significant additional disclosure. If the original application had been filed as a real application and not a provisional application, there would be no requirement to update best mode through the entire pendancy of the application. As a result, significant amounts of money/effort can be saved and any new developments in the subject technology can be protected as trade secret if so desired.
Wow, I'm really convincing myself provisional application are a bad deal -- more so that I thought.
@Bob Roberts: Yeah, I see that, too. Big, huge application and less than a week to get a priority date. If they have some document(s) that look(s) like it could be enabling but would never be filed as a real application, I can file that as a provisional and buy myself (and the client) some time to organize the thing into the form and flow of a US patent application. But I explain the requirements of Section 112, p 1, to the client and explain the risks and make sure they understand them.
I have to be careful. Sometimes clients think I'm scolding them. Then I explain that I want them to just not blame me if things don't go well for reasons that were beyond my control, just trying to make their expectations of me realistic.
And, I make it clear that I don't recommend the approach of just filing whatever documentation the client has on hand as a provisional. I've met other practitioners who actively recommend that approach. I don't agree with them, clearly.
@DogDayPM: I like that idea. It avoids the best mode problem I mentioned above.
Regards.