What process can be used to give a high-level overview of how work is progressing or help compare key tasks across projects?

A milestone is an essential project management tool that signifies a specific point in time within a project lifecycle. It is used to highlight significant events or achievements and can provide a high-level overview of how work is progressing. Milestones serve as checkpoints that help project managers and stakeholders quickly assess whether the project is on track, focusing on critical deliverables and timelines without getting into granular detail.

By establishing milestones, teams can effectively compare key tasks across various projects by aligning them against these crucial points. For instance, if multiple projects share a common milestone, it allows for direct comparison of progress across those projects, facilitating a more strategic view of overall performance and resource allocation.

The other options, while useful in their contexts, do not specialize in providing such a broad overview. Single use approval and existing approval refer to specific processes related to validating project components, and task lists are more detailed and focused on individual activities rather than a high-level summary necessary for comparative analysis.