The significance of project milestones in development lies in providing clear checkpoints throughout the project lifecycle. These milestones help track progress, facilitate communication, and ensure that teams adhere to established timelines. By breaking projects into manageable phases, stakeholders can assess performance, allocate resources efficiently, and mitigate risks effectively. Successful achievement of milestones often results in enhanced team morale, better resource management, and ultimately contributes to the successful completion of the project.