If a ship uses EM in SFC3 then it suffers a self-imposed -33% penalty to hit with all its weapons (except mines of course). The defensive benefit of EM in SFC3 is unknown, though I'd bet that it is straight from SFB, as a "+2 shift" (i.e. -33% to be hit). Note that EM takes no energy to use in SFC3. There's no reason to not use EM as much as possible, IMO.
Apparently, Taldren thinks the general public is better off being ignorant of essential game mechanics such as EM.
Ignorance = bliss?
Perhaps...
Frankly, I don't care anymore. Those who wish to educate themselves must gather some in-game statistics. I wouldn't count on Taldren to provide any technical info beyond the paltry amount thus far released.