I was actually discussing this today in a recruitment meeting. A lot of branches, like mine, need time to onboard the influx of new applicants. It can't be done hastily or at all once. That means some current applicants could be waiting for months. Comrades in a branch are responsible for keeping in touch with all those people and evaluating them for candidacy, and it's easier to do so if you join the Action Network. You'll have a consistent means to engage with party work, familiarize yourself with the organization, and you'll demonstrate your seriousness to the comrades, which is important in prioritizing recruits. We can't be taking on flaky people, basically.

So, I'd encourage you to sign up. If you're positive you want to join, it'll prepare you for that. If you aren't, it'll help you figure that out.