The reason why they don't want you to attend while waitlisted is because they don't get paid if you're waitlisted, and the chances of someone dropping out of it is low (a lot of students with financial need even get free LARC, lame!). They usually recommend you to join a different LARC tutor for the same course... Just recheck webreg.
To be honest, LARC tutors are no different than Department Tutors (who teach free). The quality of the tutoring is from the individual-- so don't be fooled into thinking quality tutoring is more costly. The main difference is that LARC tutors tend to go by a curriculum and rehashes the lecture points with some problems, while department tutors free-style and pick the main concepts/problems that will show up on the exam.
Gchem Department:
https://eee.uci.edu/09f/40978/
Ochem Department:
https://eee.uci.edu/09f/40981/