Coursework at community colleges often transfers to the basic classes at a state university at a fraction of the cost. A 12-hour undergrad semester at the state school near me is ~$8,200 in tuition alone not including a few hundred dollars in fees and a few hundred dollars in books. 12 hours at the community college nearby is $744 including books, tuition, and fees. The majority of the first three semesters in an engineering degree from the state school will be mostly transferrable classes available at the community college, the fourth semester will be pretty mixed between major related classes that can't be transferred and transferrable classes.
Starting classes at community college and transferring to the state university later is a good strategy but is often ignored.
It's a fine strategy, but the critical words there are "transferring to the state university later."
Critically, a community college will NOT cover beyond the first 2-4 semesters of a university BS degree.
This is also not a sustainable strategy. At an engineering school, 100% of freshman will take calculus, and a 300:1 lecturer to student ratio is super-profitable (even factoring in recitation instructors and TAs). The cost is in the more specialized courses, which have at least as much planning, drafting of homework assignments, etc., and where those go obsolete much more quickly.
If everyone did this, price structures would need to adapt. Universities generally use large freshman classes as moneymakers to support smaller, more expensive, more specialized junior, senior, and graduate courses.
As a footnote, things like AP exams and online courses can do similar, also at low cost.
The better community colleges have honors programs that routinely graduate and then transfer their graduates into the best schools. Makes for quite the tuition optimization.
Starting classes at community college and transferring to the state university later is a good strategy but is often ignored.