It is fine for finding the docs. However people use it to find quick, frequently out of date or just wrong solutions on the net.
For example. If you are using the babel compiler and its plugins you will fine lots of answers that are wrong on Stack overflow because they were written when Babel 6 was the major version was popular. Whereas reading the docs (the doc site is quite good IMO) will get you the correct answer every time but comes much lower in search results. Using the babel 6 suggestions can lead you to into some sort of NPM hell.
For example. If you are using the babel compiler and its plugins you will fine lots of answers that are wrong on Stack overflow because they were written when Babel 6 was the major version was popular. Whereas reading the docs (the doc site is quite good IMO) will get you the correct answer every time but comes much lower in search results. Using the babel 6 suggestions can lead you to into some sort of NPM hell.