Inscriptions are similar to weaponmods... in prophecies and faction you cant change the damagemods (like +15%^50) or the casting/recharge times (from staffs, rods, etc). With inscriptions you can change those too, but only for weapons that have an inscriptionslot.
Incription are very good tools in Nightfall allowing you to change mod for weapons, shields ect. You can change a weapon from Damage 15% while health is above 50% to reduce poison duration on you by 33% ect.
