it completely depends on your current diet. If you are eating a significant amount of fish and nuts, you dont really need to supplement your diet with EFA's because you are getting enough from your regular diet.
nuts and seeds provide you with Omega-6 and fish provides you with Omega-3. Both are essential in a good diet.
They proportedly have some muscle sparing effects. If you add them to a meal in the form of crushed seeds instead of in the oil form they add fiber to your diet.