When your schedule is ready to perform a Critical Path Analysis, you must check if the network of activities is a nice closed network (all tasks have a predecessor and successor except for the start and finish milestones) and you should do a check on any dangling tasks.
What is a dangling task?
A dangling task, or a 'dangler' is a task or milestone that is not connected on both sides and as such will not be recalculated when other tasks in the schedule move. If you have a dangler it is hard to trust your schedule and you need to take more manual actions to have your schedule up-to-date.
In the template that is delivered to everybody as part of our e-course, we have create a custom filter that shows all tasks for which there is either no predecessor set, no successor set or neither are set. You could create this filter yourself of course by going to more filters in the filters menu.
Tip: use it as a highlight filter to include the context of the danglers.