I have often wondered the same thing. Blessed seems to have no particular effect. My guess is that in the description of certain monsters, there is a section that will describe the special effects a blessed weapon will have on those monsters.
Some creatures, especially evil outsiders or more specifically demons and devil are vurnerable to 'blessed' weapon. Check the MM for more information on this.
I know about the whole "Rakshasa - Blessed crossbow bolt" thing. Is there a vulnerability classification for this? Or is it simply a case by case basis?
I know about the whole "Rakshasa - Blessed crossbow bolt" thing. Is there a vulnerability classification for this? Or is it simply a case by case basis?