Regarding IGETC, it is nice to have completed for most UC campuses and majors, but major preparation should generally take precedence over completing IGETC.
If you do not complete IGETC, you will have to complete the general education requirements of the campus you transfer to. While the UCs often have general education requirements that are less voluminous than IGETC, they may differ from each other significantly, so you may have to carefully consider which pre-transfer general education courses to take to maximize usefulness if you do not complete IGETC.
For CSU, the general education requirements closely resemble IGETC (but note the CSU / UC difference in IGETC where CSU requires oral communication and UC requires foreign language).