The dev doesn't describe their plugin very well, so here's the description:

it makes it so any projectile does an extra amount of damage when it hits an entity. by default this damage is 0.5, so all your projectiles will do an extra half point of damage.
i don't think this plugin does enough to be worth using

i think you can make the plugin a lot more useful by doing the following:

keep your configurable damage value

add a section to the config allowing admins to set a specific damage value to specific projectile types. like arrows probably should not get this buff, so that's set to 0. this value would overwrite the previous configurable damage value you currently have.

to go a step further, allow admins to configure these damage types specifically towards certain entity types. this would overwrite the previous two values.