Project managers essentially have two areas of focus when it comes to manpower support:
Knowing that they have enough of the right resources to execute the amount of work planned, ensuring they aren’t caught short-handed at a critical time.
Understanding when those resources are needed—and when they’re best used—so they don’t have expensive labor resources onsite without anything to do.
If the team isn’t adequately staffed with the right level of labor resources to complete the amount of work being scheduled, the activity durations will ultimately take longer. This often leads to some of the project’s scope being sacrificed toward the end of the project as the team runs out of time leading up to the target completion date.