There are several test techniques which can proof very usefull from time-to-time.
Although some senior testers say: "it's better to learn on the job and from experience". To my opinion it's also very usefull to proof, with certification, that you're able to apply test techniques.
The way I see it, is that being able to apply test techniques is just one of the rings you can apply when talking about 'the book of five rings'.
It means that he does whatever it takes to get the facts on the table. When he needs to discuss to a programmer, he asks questions to a programmer. If he needs clarification of requirements, then he asks the questions to the requirements engineer.
If he's uncertain about the correct outcome of a test, he does whatever it takes to take away that uncertainty.
In the end he supplies the business with the information that they need and he does whatever it takes to get that information right.