According to Military.com, here are 5 Great Reasons:
Your ASVAB score is good for two years — for ALL branches of the military. Even if you aren’t interested in joining the military when you take the test, a lot can change in two years, so why not do your best.
This is your best chance to obtain a high-test score. With Math and English fresh in your mind there is no better time to give it your all and see how smart you really are. Math for instance gets harder and harder to recall the less you do it, so test while it is still fresh on your mind.
Your scores are not only used to determine which service you are qualified to join, but also which jobs within that service you are qualified to do. The higher you score the more career options you have. In addition, your score can directly affect your eligibility for bonuses and money for school.
Some find the “Student” version of the ASVAB easier. If you have to retake the ASVAB you will be given a different version. You may find the other three ASVAB versions tougher than the one you didn’t take seriously.
The “Student” ASVAB is a great career assessment tool that can help you identify which career areas best suit you. Because this is an aptitude test it doesn’t just tell you what you are currently good at, it will also tell you what you may be good at learning. You may know nothing about electronics but your scores may say you have the ability to learn electronics.