What would be a reason for shortening a leg in a trackline?

Shortening a leg in a trackline is often necessary to adjust for environmental changes. This can include factors such as shifts in currents, wind conditions, or visibility that may affect the route taken during a mission. When environmental conditions alter, it is crucial to adapt the planned route to maintain operational effectiveness and safety. For instance, if strong currents are pushing the vessel off course, shortening a leg can help realign the vessel with its intended track, ensuring that the crew remains on a safe and efficient course despite the changes in the surroundings.

While other reasons might have operational relevance, they do not directly correspond to the immediate need for route adjustment based on real-time environmental data.