Bukkit

Enchantment Changes

Efficiency

When enchanted on an axe, attacking a mob or player with the axe will cause nearby entities (excluding the attacker), with a max count, to take a proportion of the damage that the original defender took.

If you count the damage dealt to every surrounding target, it becomes more effective than Sharpness swords when in a group, especially if the axe has Sharpness enchanted on it. This can be used to fight against players teaming to gain an advantage over you.

Blast Protection

Armor (or skulls, pumpkins, whatever can be worn on the player) enchanted with blast protection will increase or decrease (depending on your configuration, by default reduces) knockback taken. Negative levels on the enchantment will do the reverse.

Increased knockback can be used to flee from attackers, while decreased knockback can be used to prevent fall damage, become resistant to combos (where a player attacks the target then steps back, making them out of hitting range, while the knockback pushes the target backwards), or get closer to a bowspammer. Ideally it is good to have at least 1 armor piece with blast protection on it to help make your attacks more accurate.

Protection

Balanced Enchantments applies a speed reduction, by default 1% less speed per level of protection. This allows for weaker players being attacked to have a slighter chance at running away, or play as a light-armored, swift unit instead of a heavy tank.

Enchanting armor with protection, if diamond, can make it vastly more effective. Full diamond armor can resist 80% damage, meaning essentially 5x more health in combat, and full protection IV diamond (according to http://minecraft.gamepedia.com/Armor) can resist 88% to 96%, which means 4-12% of the initial damage. At the 96% protection, 25 normal hits are required to deal the same damage as a hit while the defender has no armor. By far, in normal combat Protection is the best enchantment you can get. That shouldn't be removed, but instead be balanced, to make room for other fighting styles.

Protection can make you last longer in battle, but will make it harder to flee or chase someone.

Smite

Blocking a melee attack with a smite sword will apply weakness and slowness for a short period to the attacker.

Smite swords are only useful in PvE. Parrying helps bring a use to smite and move away from clickfest fights.

Bane of Arthropods

Attacking with a BoA sword will poison whatever it touches.

Extremely useful in "god" battles, where physical damage is majorly reduced for both sides. Although the DPS (damage per second) of the sword is low, by default one hit can deal 8 additional damage by poison. Poison can help in god battles, although it isn't fully reliable, as a sharpness sword could likely reduce more health in the given amount of time.

Feather Falling

When sneaking, players with feather falling boots will move faster, closer to walking speed depending on the level. Taking damage or interacting with the environment or items will end this buff, and the player will need to re-sneak again for maximum speed.