Henry Laurence Gantt, a mechanical engineer and management consultant, invented the Gantt chart in 1917. A Gantt chart is a graphical representation of the duration of tasks that project managers use
to plan and schedule projects. The Gantt chart's horizontal bars show the entire time period of a project, broken down into shorter increments of days or weeks. The vertical axis shows the tasks. Managers favor Gantt charts; however, using them has advantages and disadvantages.
An advantage of Gantt charts is their graphical overview. Businesspeople have become quite familiar with the Gantt chart's graphical representation of project timelines and milestones, and they like the fact that they can clearly identify the steps of a project. Because tasks are often represented by a series of different color bars, members of a project management team can identify their jobs in a project at a glance.
Gantt charts are presentation tools that show what the key milestones of a project are. By seeing how project managers have allocated and scheduled each resource, the entire project management team stays on the same page about expectations and deliverable due dates. This ability to illustrate milestones is also a helpful tool for senior managers preparing status reports; they may not want to decipher detailed reports. A Gantt chart gives them a way to work out the critical path.
A disadvantage of Gantt charts relates to task dependencies. When project managers are illustrating tasks in a project, sometimes they want to show how the tasks depend on one another. Unfortunately, the Gantt chart's format doesn't allow for this. To alleviate such problems, project managers can illustrate any constraints relating to the tasks by adding vertical lines, but this limited solution doesn't provide enough information about key dependencies, and it doesn’t enable project managers to verify the dependencies.
Projects are not static: some changes may be expected as you go along. However, Gantt charts are not flexible in that way; they can't accommodate such changes. Project managers must finish all the estimates before they can produce the chart, so if estimates change, then they must redraw the chart. Also, Gantt charts cannot illustrate several scheduling possibilities in the same chart, nor can they easily indicate resource assignments.