If you are a minimalist flier, you are in luck when flying American Airlines. If you have no overhead luggage you will be able to board between Groups 1 and 2. Your carry on item must fit in the seat in front of you to qualify. I actually like this new policy as those fliers take up no time in the boarding process and take their seat quickly. It is putting your luggage up above that can take forever!
You will still be boarding after quite a few people, including First Class, Business Class, Uniformed Military, Executive Platinum, Platinum, Gold, Priorirty Access, and Group 1. On those Monday morning and Thursday evening flights, that could account for more than half the plane! Still having the ability to board sooner than later if you desire is a nice perk.
You can learn more about this process and just the general boarding process for American here.