Guide
It makes sense when software supports an important process and off-the-shelf tools would create more expensive long-term compromise.
Custom software is not the right answer to every problem. If the process is standard and an existing tool fits well, building from scratch may be unnecessary.
But when the workflow is specialised, integration-heavy, or trapped in manual workarounds, custom development is often the stronger business decision.
A good outcome rarely starts with an endless specification. It starts with a practical frame that can be tested in the first delivery phase.
The biggest problem is usually not a lack of specification text. It is weak prioritisation and an unclear goal for the first phase.
The guide should help you make a better project decision, not add another document with no delivery impact.
Yes, if it supports a repeated high-value process and standard tools force costly workarounds.
Yes. That is often the most sensible way to validate priorities without overshooting the investment.
Yes. In practice that is often the strongest model.
Next step
Share the context and I will tell you whether the project is a fit.