What Is Float?
There are two kinds of float. Free float, or slack, is the amount of time a single activity can be delayed without delaying the ES of any subsequent activities. Free float determines the pressure that one activity puts on the next activity.
Total float is the sum of free float for each activity in a particular path. It is also the amount of time an activity can be delayed from its ES date without delaying the project finish date. Total float often changes as the project progresses and changes are made to the project plan.
Project managers use total float to adjust schedules and resource allocations. When it is used to adjust resource allocations, the process is called resource leveling.
Total float is an important indicator of project status. If total float is greater than 0, then slack time is available. If total float is 0, then the situation is critical. If total float is less than 0, then the project is already behind schedule or critically late.