It will make the game easier the further in you go -- at the beginning it will make no difference. The THAC0 tables determine whether you score a hit when you attack (ToHitArmourClassZero) on your dice throw. The un-nerfed tables allow your character to progress all the way to armour class 0 -- lower is better.

Let's say that your character's THAC0 is 17. When he/she attacks, a 20 sided dice is thrown based on his/her THAC0 and the enemy's AC (Armour Class). If the enemy's AC is 3, then your character must roll 14 (17 - 3) or greater To Hit the target. So you can see that if your character's THAC0 was 4 in the above example, the result would be that you only had to throw a 1 (4 - 3) or greater. Smaller is better with THAC0, as with AC.