Blades Defender provides a friendly creature in the lane opposite to it 2 extra points of health. This is most effective when applied to a creature that either deals a high amount of damage or has the lethal keyword or has a useful effect but has little health itself. Providing such a creature with extra health will increase its survivability and thus can be used to greater effect. Blades Defender's effect is also useful when applied to Guards, making them more resilient and further preventing other creatures and the summoner themselves from being attacked by hostile creatures in that lane.
Blades Defender's effect cannot be used on friendly creatures in the same lane as it or if there are no friendly creatures in the opposite lane. As such, is best played to the opposite lane to whatever creature would most benefit from the effect.