There are many reasons you should put yourself though the special kind of stress that accompanies presenting your research. This post will cover two.
1) To build your resume or CV. Whether you apply for a fellowship, scholarship, or med/grad/prof school, the more presentations you have to list the better off you'll be. Most selection committees rank research presentations as a quality-rich activity.
Whether your poster is for an undergrad research symposium, or a professional meeting you should take it seriously. The poster you create represents you. Your best work, and your lab. The quality represents the value you find in your research project, and how much you appreciate your research supervisor’s efforts. The poster you create also sends a message to the PI about how much you value the research opportunity you’ve been given.