This is not always true. Some state universities (e.g. in California) have extensive articulation agreements with same state community colleges, but much less so for any four year schools.
On the other hand, colleges and universities in areas where community colleges are generally limited in transfer preparatory academics may have a worse view of community college courses.
Yes, a taste of true college courses (as opposed to college frosh level material in high school AP courses) can give you an idea of what college courses will be like before you dive completely in when you go to college full time. College courses require better time management and self motivation, with less hand holding and progress monitoring than in high school.