Broadly speaking, we have two types of project: One-Time and Ongoing. A one-time project uses your classic project structure with a clear kickoff and delivery. Ongoing projects involve continuous work on a single area or client account, touching on many individual outputs over an undefined period of time.
Sometimes an ongoing project will spawn a separate one-time project. For example, Finance is an ongoing project with no defined end date (we will always be working on Finance). But there may be a particular one-time project within Finance that we conduct, for example, modernizing our accounting system.
One-time projects can be tracked within the normal ongoing project methodology, for example, by creating several tasks that are related around a common need or effort, and working on them over the course of a few sprints. They can also be tracked as fully separate projects. This is up to the discretion of the project manager.
With client work, we have a standard ongoing agreement structure that involves both a fixed “Core Retainer” and then separate hourly or per-SOW work.