—from the PI's desk
No matter if your long-term career goals include research, medicine, or using your STEMM degree primarily for science communication, policy, or another direction, participating in an undergrad research experience is a unparalleled opportunity. This is in no small part due to the personal and professional development you gain from the exposure to in-depth, experiential learning--especially one that takes places over the course of a summer.
In addition to learning new research skills, communicating your results, and making a discovery to solve a problem or answer a question, you have the opportunity to earn a recommendation letter to support future applications for grad, medical, or professional school, and graduate fellowships.
However, if you are early in your undergrad career, you may not need that letter until a few years after your summer research experience. Sure, you could come back to your mentor after that time and request a recommendation, but that approach has some major disadvantages. Most importantly, the more time that passes between when you leave the lab and when you ask for a recommendation letter, the fewer the specific details about your strengths and successes your mentor is likely to remember—and it’s those specific details that can turn a strong letter into an epic one.