Some Framer work doesn't fit into a single project. New pages come up, a template needs adjusting, or a design arrives that needs building. On-call support gives you a Framer developer to bring that work to as it comes, billed by the hour. I've worked this way with recurring clients for roughly two years, handling Figma-to-Framer builds and template adjustments. It suits agencies with an ongoing flow of Framer work and business owners who keep adding to their site.