Manuals are not really for reading cover to cover. You generally want to use the table of contents, the index, or searching of some variety (google, ctrl-f, whatever) to narrow in on exactly what you want to know. A few scenarios I find them useful:

(1) If you're getting conflicting advice from blogs and stack overflow: this is often the case when software is changing fast. Manuals are often explicitly versioned to match the software, so if the manual covers the topic you care about, going to the latest manual is a great way of figuring out which advice is current.

(2) Skimming the index: a quick way of discovering topics you can then explore in more detail either in the manual itself or through follow up googling.

(3) A manual you know and love. Over time you get a feel for which manuals you interact with are good. If a manual is good and you've gotten comfortable reading it, it's often faster to find the answer you're looking for by searching the manual directly rather than wading through a google search.