It's more of a tuning option. If you use the 1° hubs, you'll have to increase the toe using the blocks so that means you'll have more toe in on the inboard side. If you use the 2° hubs you'll have less toe in on the inboard side. It's a small change but it does affect the way your car feels, experiment with it and see what happens as I am not confident enough with my tests to explain exactly what happens when you switch.