Games : Are weapons that are "effective against birds/beasts/slimes/lizards/undead" really any better?

In Secret of Mana, certain weapons say they are:

• Effective against slimes/lizards


• Effective against birds/beasts


• Effective against plants/fish


• Effective against evil/undead/non-living enemies, or


• Effective against dragons

What does this actually mean? Does it make any noticeable difference? Does it mean they cause 1% more damage? 10% more? 100% more? Or does the game simply say they're better but they have no effect at all?