Building in public is scary. Every time you update your followers with news and progress, you're letting yourself be vulnerable, and open to criticism (sometimes constructive, other times not so). So why would anyone want to do it?
Validation.
It's easy to speculate whether or not an idea for a product is a good one, but talking about it in public with potential users is an easy way to validate an idea. If you engage with 50 people and none of them say it's a good idea and sign up for it, then you're either asking the wrong people, or it's not a great concept for a product. However, if even a small number of them sign up (say 10 out of 50), then you know you're not on your own, and can build a product that at least some people want to use. Sure, the chances are if 0 out of 50 people want to use your product, that doesn't mean no-one will want to use it, but these 50 people are crucial - if they're people you interact and engage with regularly, then they're going to be your biggest soundboard. If they like your product, they're likely to share it amongst their following, and their friends and family. But if they don't like it, they probably won't. And that's totally fair.
Early User Base
One reason I wanted to do it was to help grow the potential user base. By talking about it often and sending out the link to get people registered for it, I've got at least some users before the product is even launched. Some have even given feedback on how to improve certain aspects of the app, before it's even launched. Some feedback is very nit-picky, and contradicts other feedback from other users, so trying to figure out which feedback to take into consideration when updating the app is tricky, but the fact some users are invested enough to provide constructive criticism is actually encouraging. By saying they would like the app more if it did XYZ, it's proving that people like what I've built so far, but it's important to remember you can't please everyone, even if you're building a niche app.
Cheerleaders
Every time I post an update about the app, even if it's just a "I added a new feature" or "I fixed a bug", I get people liking, retweeting, and commenting, cheering me on. It's a bit of a buzz that people are excited for the app, as well as a nice little ego boost, which just opens the floodgates of positivity and motivation. If I don't post about it for a couple of days, I get the odd message asking if everything is ok, and if there's any update. It's encouraging, and heart-warming.
Getting Over Fear of Failing
What if my app fails? What if after months of hard work, blood, sweat, and tears, and endless testing, people finally get to use the app, and it fails to live up to expectations, and people stop using it? Then I've learned what not to do when I build and launch my next product (and you can guarantee there will be a next product). The best way to get over any fear is to confront it. If I let my fear of fapubliccilure rule my work, I'll never release anything.
Accountability
By publicly announcing, discussing, and promoting my app, I'm creating accountability. I'm forcing myself to work and release the app, as that is what people are expecting me to do - even those who aren't particularly interested in the product. After all this time, if I fail to deliver anything, it's going to damage my reputation as a developer. Delays happen, yes, but not releasing anything can be a career killer.
Conclusion
There are many fantastic reasons why I'm building in public. From validating my idea, to getting an early user base, to actually forcing myself to release something. There's several reasons why you might not want to build in public, which I'll be discussing next week, but I hope this article has helped inspire you to build in public.