Yes, increasing one's n-3 consumption is just a recommendation but it is a recommendation backed up by research. So far most of the research I've seen has not focused on flax seed oil. Fish oil is a better source of n-3 EFAs, if it wasn't so expensive no one would be bothering with flax. However the n-3 EFA in flax is converted in the human body into the same EFAs found in fish oil, unfortunately the process for doing that is slow and may not convert enough for optimum health. Furthermore the process is defective in some people. There is current research using flax seed oil so in a few years we may better know if it can be used to fill our n-3 needs. Personally I eat fish, flax seed oil, fish oil and several sources of n-6 EFAs. I don't go out of my way to get n-6 since like most Americans I am awash in the stuff. If you are concerned that you may add too much n-3 EFA to your diet just take a couple of fish oil capsules a day, if you are an average person any additional amount will make a large positive difference.
Here is a little of the latest news I've seen on the subject.
A lot of snippets on the subject, mostly why developing children and pregnant women NEED EFAs. But be careful since the mix of EFAs must be correct or problems can occur, research the topic well.
"They are part of a growing body of science indicating links between diets low in omega-3 and such problems as bipolar depression, suicide and post-partum depression in mothers of young infants.
Heart researchers have believed for decades that modern diets low in omega-3, and high in a related group of fatty acids known as omega-6, are associated with increased risk of heart disease.
Evidence that mental and behavioral problems may also stem from omega-3 deficiencies is more recent. But according to Hibbeln, chief of an NIAAA biochemistry laboratory, the evidence is dramatic."
http://www10.netrition.com/cgi/news.cgi?file=20020418080700_0
A New England Journal of Medicine article about EFAs and heart disease.
"Background Experimental data suggest that long-chain n-3 polyunsaturated fatty acids found in fish have antiarrhythmic properties..."
http://content.nejm.org/cgi/content/short/346/15/1113?query=TOC