The Effects are used for specific abilities and are purely used for visuals. Check out Starfall for instance, it uses an Effect as part of it's art.
Buffs on the other hand are those tiny icons that appear in a unit's status bar below it's Armor. Berserk applies the "Berserk" buff, Bloodlust applies the "Bloodlust" buff, etc...
Buffs also contain the effects of the ability. So if you dispel/remove the Bloodlust buff from a unit then it loses the bonus attack rate and move speed.