Assets depreciate over time. So do ideas.
A good product manager learns to listen to the needs of the market and faithfully records them (actually a lot of them don’t. I am sure you are not one of them) to feed the roadmap. Sadly, engineering resources typically are fewer than what is needed to satiate all the needs. Backlog builds. And here is where the trap-door opens up.
Product Managers often carry forward their backlog inventory of ideas into a subsequent development cycle. FIFO or LIFO? Personally, I am dead against the deadwood FIFO and lukewarm towards LIFO. FIFO is a straight reject because more an idea asset stays in the backlog the more likely that it has depreciated in utility value. What was a strategic differentiator when first recorded as a need might just be either a me-too thing or worse – something akin to picking nickels in front of a steam roller today. LIFO stands – a priori – a better chance because they haven’t yet wimped out by the sands of time (hopefully).
Creating a product roadmap is a much involved process than just collating a backlog. Relevance of each idea must be evaluated with the market and competition before engineering resources are committed to build them out. Yes, it does place an additional overhead on Product Managers but would you rather find out those irrelevant product ideas or leave it to the market?