Its really pretty simple. You have to monitor the critical path because that is where the immediate delays will appear. You have to monitor the near-critical path because that is where delays will take over the critical path, likely in a mid-period critical path shift that will occur between updates and could take you by surprise. And you have to monitor the non-critical path because that is where disruption happens, where work slips to the end of the project and stacks up, and where significant disruption and delay will occur while you are watching the critical path, especially if the network is not really well done.
The lack of good resource logic often causes many of the non-critical path problems. Without resource logic, similar trade work will be allowed to stack on the schedule, while no one really watches to see that the schedule now shows a need for three electrical crews, then four, then seven, then nine, until rapidly there are not enough resources to work concurrently on all the activities needed. With poor resource logic, you cannot count on float dissipation reports, you cannot count on critical path analysis, and the only remaining way to monitor is for good, trade and location specific earned value monitoring. Even then, it is likely that the project will not provide adequate early warning of resource problems.
I suggest that all schedulers run a late date sort on their baseline schedules, then organize the schedule by week, and starting at the end of the project, look at how much work is planned to happen every week, especially in similar trades and specific locations. Usually, I find that the baseline plan is unworkable, so that all it takes is a couple of minor slips in progress to put the project schedule in a position where concurrent work by trade and location is overwhelming.
If engineering, procurement, and owner responsible work are all missing or inadequately modeled, the network is not capable of providing the robust and effective monitoring tool.
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