Task Network is a form to represent (visualize) dependency between actions to show how they are arranged into the correct/planned order. Example of a task network is a project activity diagram or WBS where particular tasks are linked up to each other to show their impact within project plan. By using task networks you can make your working plans more comprehensible and easy-to-grasp: it is a way to schematize (map out) your future efforts and represent them in a vivid format that provides opportunities for optimization.
Task networks can be composed on every project that is complicated enough to have more than one line of activities at the same time (it has some tasks running in parallel). Task networks provide you with an opportunity to review how the tasks can be put into parallel to decrease duration of the task schedule (schedule compression), and also give you a base for constructing risk and resource break-down structures where you can associate each activity or work package from a network with these matters to overview your future needs in supply or threat mitigation.