Beta testers are helpful in more ways than one. Not only do they provide more hands for testing, but the larger the pool, the more varied the opinions are and the more suggestions the team gets.

One thing specifically is that sometimes a dev team is so close to a product that they can't see it from anything but a certain perspective. They are sometimes surprised by the opinions presented by their testers because they never thought of something in that way; fresh eyes are needed to "see" something properly and that's where the testers come in. We can point out that something doesn't make sense, or that something would be improved by presenting it differently, or that something is perfect the way it is and don't change it.

The continual influx of fresh eyes needed is probably one of the reasons that invites go out in waves, rather than inviting a bunch of people all at once. So if you haven't been invited yet, don't give up hope - keep an eye on @DragonAgeKeep for notices of when the invites go out. And don't forget to check your spam folders :) They've recently said that they are trying to get everyone in who wanted to be in prior to going live, so definitely keep checking (no pun intended :)).