Learning the princples and philosophy conveyed in that book helped me tremendously in my career (as a software engineer). Thanks people at Google for writing and open sourcing it.
Seriously. A lot of the book was influenced by Social SRE who had opinions all out of proportion to their own importance and success. At the time, there was some doubt about whether Social's pet theories belonged in the book, considering the varying practices and beliefs of other SRE groups supporting products that people actually use.
This is related to my rule that anybody can title their doc "Best Practices" even if nobody subscribes to them.
Example: the section on backend subsetting in distributed systems is not current. If you wanted the current Google practice you need to read "Reinventing Backend Subsetting at Google"[1], and there are other interesting publications from other organizations.