What are some limitations of the PERT/critical path approach?

Question

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The PERT/CPM management places a lot of emphasis on critical path activities. This can mean an excessive focus on them that leads to not enough attention being paid to other tasks. Just because they have some slack doesn't mean they can't come in on time. Additionally, time estimates are subjective. Even though they've gone through a nifty formula there's going to be significant variation on the actual time it takes to complete tasks. Also, constantly keeping track of time estimates and recalculating the critical path and other metrics can be very time consuming.
Key Takeaways: Project management instructors and manuals seem to love PERT/CPM. We just want to point out some of the drawbacks. In some cases, the attention to detail and effort required will not yield a significant incremental improvement in your project processes. A great part of it depends on whether or not your project is the type where discrete tasks can be estimated individually with any accuracy.

What Are Some Limitations of the PERT/critical Path Approach