[Taqwus]

Besides, a 3- or 4- star unit already has a significant advantage over a 0- or 1- star unit. Look at the table on page 5 of the manual: a contest between two open die rolls with no net modifiers is at 46% chance of success, while a difference of 3 turns it to 70%.

att 13 vs def 10is a difference of 3; 70% chance of hit
att 10 vs def 13 is 24% chance of hit; roughly 3:1 ratio

att 10 vs def 10 (before 3 star difference) is 46% of hit


There's also effects on precision and morale. That morale boost might come in handy against Fear and Awe effects.