On the other hand, when they ask for something off the roadmap, we get into more complex issues (is this market-demand data, or custom work?) Particularly for grunt-level custom work (say, adding a support for tracking data on a niche wearable device that we don't currently support) there's a lot more questions that follow.
One of the most insidious of the latter, IMO, is that if it's just for one contract, then we're either hiring contractors/outsources (expensive, high management overhead), hiring new engineers (risky to grow headcount on a whim), or redirecting resources to tasks that are likely to have both lower ROI and provide lower growth for the re-tasked engineer. At our small size and need for high-quality people, I consider this to be a real cost too.