Beta is truly for people who want to "test" game, usually it has nowhere near the content amount of final version build, isn't like The Twist or something where it is just a matter of fixing bugs between first beta and final build.
Personally I never touch them because I don't have the time to be assed to play a non-final build.
Each version of HH is released as followed.
1 Week after v0.x starts development, the Alpha ($20+) build is released
1 Week after that, Beta #1 ($10+) is released
Every week after that, another Beta is released until the version is done (Usually 3 weeks of Betas)
Once the version is done, the $20+ Pre release is released
A couple days later, the $5+ Pre release is released
1 week later the public gets access
Every week of the releases above is a week where I'm working on new content that hasn't been started a week before (Except for the $5+ pre release). Like Klx said, I'm not just releasing bug fixes for a month. Patrons have something to come back to every week to test and provide feedback to.
These builds are very important to finding bugs, and very important to giving me feedback. Getting feedback when the version is still in beta lets me change things, rewrite things, or just completely remove things that were bad. Through people finding bugs, and providing me with feedback, it really helps the public releases be as best as they can be.