Though initially low damage and accuracy, when upgraded, archers should be a staple in every army. Ranged support can turn entire battles, eliminating lightly-armored, but high-damage units before they can get into melee.(e.g. cavalry, longaxes)
Research in the campaign replaces/upgrades Bowmen with Longbowmen, and later Master Longbowmen.
Masterwork Armor is useful to give some small survivability, as they have no defense, and a measly 5% resistance by default. Swift arrows can be used to increase damage output at important times. Swift Arrows can be used to increase damage output at key moments in a battle; e.g. multiple archers can actually break an impending cavalry charge when all using swift arrows.
Aimed Shots should only be taken if you suspect you'll be using them against heavier units. Against light infantry or other bowmen, it is actually a hindrance if left toggled on.