Total Float would not be as useful a measurement if it could only tell us what was critical. It also tells us how far away other activities are from becoming critical. We call these ‘almost critical’ activities, “near-critical.” Any decent CPM analysis also looks at near-critical activities.

Longest path is a more accurate measurement of the critical path than just using total float. The weakness of using longest path over using total float is that longest path only tells you if an activity is on or off of the longest path. You have no idea how far a non-longest path activity is from joining the longest path.

Multiple float paths tries to answer the question, “what is my second-most longest path, my third-most, etc?” I hope that this helps. Good luck!