An idea tells you what to do; a requirement defines what needs to be met; and a concept presents alternatives for how it can be done. Confusing these three concepts is one of the most common causes of delays in the development process.
Scope
Requirements gathering and prioritization: Compiling requirements from customer, regulatory, manufacturing, service, and sales into a single list and classifying them as mandatory/preferred/optional.
Requirement traceability: Tracking which design decision, test, and product feature each requirement corresponds to. The answer to the post-launch question "why was this feature there?" lies here.
Comparing alternative concepts: Comparing different technical solutions that meet the same set of requirements in terms of cost, time, risk, and reuse.
Reusing existing components: Determining from the outset how much of the existing materials, modules, and platforms the new product can utilize. This is the technique that most effectively reduces portfolio complexity.
Concept to proposal: Presenting the chosen concept along with a business case study to the decision-maker.
The key point: reuse.
Every new material code used in a new product adds a permanent cost to the portfolio: a new supplier relationship, a new quality control procedure, a new stock point, and new regulatory documentation.
Making the existing component catalog searchable during the concept phase means the designer can get an answer to the question "does a similar part already exist?" within seconds. This single habit is the practice that most reduces portfolio complexity in the long run.
Benefit to the customer
Scope creep is controlled from the start.
Eventually, the "this wasn't what we wanted" situation is eliminated.
Regulatory requirements are considered at the beginning of the design process, not at the end.
The variety of parts and materials grows in a controlled manner.