If you are only one course away from IGETC, you may as well complete it. UCSC allows it to fulfill lower division general education requirements: https://admissions.ucsc.edu/why-ucsc/faq/student-transferring.html . Also, having it completed may be useful if you transfer to some other UC or CSU.
The non-recommendation for IGETC for CS is presumably to get transfer applicants to focus on the major preparation courses as their main priority.