Completing a project requires resources like people, buildings, materials, equipment and so on. By assigning resources to activities you can determine the number of resources you will need, when they will be needed, and what amount of money they will cost you. To manage your resources efficiently you should add them to resource groups in IFS/Project, and assign calendars showing their availability along with cost and limits.
You do not have to assign resources to activities to complete a project in IFS applications, but doing this in conjunction with scheduling your project in a 3rd party planning tool like Ms Project or Primavera Project Planner makes it easier to complete projects within budget and time.
Microsoft Project and Primavera Project Planner factors resources into the schedule and provides information to help you better manage them, such as whether they will have to work overtime and how much each resource has cost to date according to plan.