In old haven I used to always spam my marksman so I could shoot stuff. I just liek doing it. I was lookign at the wiki and marks seems kinda poopoo now. This is all it says.
Marksmanship
Increases damage dealt by range weapons by comparing your Perception*Marksmanship with target Agility*Marksmanship
Softcap for crafting the Hunter's Bow , Sling , Bone Arrow and Stone Arrow.
Equipment which modifies Marksmanship
Is raising it worth the damage gain? Not sure what the stats of mobs are.