College courses require students to work independently without much assistance from instructors. Self-guided research is the norm. Pre-college courses equip students to know how to seek out reliable reference materials.
A college instructor may distribute a syllabus to a class of 400 students that outlines what texts should be read and when, and it also states when assignments are due. This enables the instructors to teach more efficiently, and they can set expectations up-front. A student who has taken college-level courses before knows how to deal with this situation.
In most college classes, the weakest link in the class will not slow the instructor's pace. Pre-college courses help students become acclimated to learning large amounts of information over small periods of time.
Although colleges and universities offer some remedial courses to fill in gaps in education, they are few in number. Pre-college courses prepare you to participate in advanced courses without using credits to learn concepts that should have been covered in a high school curriculum.
Pre-college courses may help you decide if college is right for your career path. Also, taking some early preparatory coursework may help you decide on an area of study before taking freshman-level general courses.