Tasks can be linked if they are related in some way. For example, if you're doing a new installation and have to re-attend in three months to perform an inspection, you could create a new linked task. This will give you the option to go backwards and forwards so you can see the original installation task and then the more recent inspection task.
Linked Tasks appear against both the original task and the linked one
All users in default permission groups can see that there are linked tasks (but may not be able to see the linked tasks).
Supervisors can also add linked tasks.
Managers can add and also remove linked tasks.
If you have custom permission groups, Site Administrators can enable task linking via Permission Groups > Tasks > Fields > Linked Tasks > View, Add, and/or Remove (tick as appropriate).
Create a new linked task (via an existing task)
If you're working on an existing task and want to create a new task or quote for the same client/location, you can use the Create button located at the top right of the Task window. Creating a task in this manner allows you to link tasks together to make it easier to track job history for a particular client and location.
Open an existing task.
Click the Create button located at the top right of the task window.
Select the appropriate option:
Use Client - will create a task/quote against this client.
Use Client, Location - will create a task/quote against this client and location.