Sustainability requires ongoing reform of resource production and consumption to reduce environmental harms. The main way that Information and Communication Technology (ICT) can address these resource impacts is through digital optimization. Spreng found that optimization of an industrial process either increases energy use or accelerates production or consumption. It was assumed that reducing energy use progresses sustainability, whilst accelerating production or consumption to meet market demand is consumerist and generally detrimental to sustainability. In this paper, we argue that there are two important cases in which accelerating economic processes actually has an essential role in enabling sustainability by ICT: (1) when the process drives the production and adoption of an environmentally beneficial product such as a solar panel, often referred to as "cleantech", or (2) when the process being increased is specific to the Circular Economy, such as recycling, maintenance/refurbishment, and sharing/reuse e.g., car-sharing, ride-sharing and tool-sharing in the Sharing Economy. The opportunities for ICT4S optimization are thus threefold: not just saving resources with efficiency, but also pushing the adoption of cleantech, and pushing the circulation of resources.