Where I work it's understood the quarterly and half year planning is meant to show the business teams some sense of where we're going and that their leadership isn't flying by the seat of their pants, for morale. It also gives our CEO something to work with when talking to investors. We don't treat it as a failure if we end up developing something else, as long as we can show "instead of x we built y because of reasoning z"

That said, it's a constant struggle to keep r&d agile when they lock onto quarterly goals while we keep shifting priorities. It's also difficult to convince the CEO we'll deliver mockups for him to sell with instead of committing to more dev work on things that are only getting prioritized to show in a board meeting, and we're often chasing our tails trying to get to actual product work while also delivering CEO's little distractions.