Tuition costs seem to be ever on the rise, and the median student loan debt for baccalaureate-level graduates in 2007 to 2008 was $19,999, according to finaid.org. Community colleges cost significantly less than four-year universities---on average, less than half per year. By living at home and taking advantage of the lower tuition for two years while you attend a community school, you can save tens of thousands of dollars.
Maybe your grades in high school weren't so impressive, and you don't think you have much chance of getting into your dream school. Earning a high GPA at a community college proves you're capable of successfully completing college-level work, and you might be able to get transfer admission into that coveted school. In some cases, it's easier to gain admission as a transfer than as freshman. That's because not every admitted freshman will return for their sophomore or junior year---some will flunk out or switch to another four- year school. Your target university will need to fill their vacant spots, and that's where transfer students come in.
It isn't always easy to decide what you want to do for the rest of your life when you first get out of high school. Two out of three students change their major at least once over the course of their college career. Changing majors at a university can delay your graduation and cost you more money. At community college, you have two years to take general education requirements and can experiment in different subjects a lot more cheaply.
Professors at universities often focus on research or writing articles for scholarly journals. Professors at community colleges may have more time to dedicate to students and are more likely to be available when you come to their office in need of help. Community college classes are typically smaller than university classes, allowing professors to give individual students more time and attention.
Not everybody is quite ready to leave home and adjust to college life as soon as they turn 18. Some students may need more time to mature---that's part of the reason why so many freshman don't make it to sophomore year at residential colleges. Taking a detour to community school in between high school and university can help make your transition more successful.