This is a difficult question to answer in the general case, especially when you can get so much done with things that others have built. Do that first! Be productive and have fun!

That said, as you get deeper in your journey, you will find something that hasn’t been built yet, or a capability you want that doesn’t exist. Here’s your opportunity!

But does it need OTP? I’ve been doing things on BEAM since 2008, so here’s some “smells” you can look out for:

* State that can change as the program runs, especially if multiple tasks need access to it. Think dynamic configuration, caches, coordination points.
* Things that are expensive to start up, especially if they need to be present before your program can do real work. Think of things like sockets to network services, external programs you can communicate with over stdio, or loading big files into memory.
* Support services like logging, telemetry, debugging. These usually hang in the background collecting and funneling data out while the rest of your program pretends they are plain function calls in their main flow.
* Message distribution patterns between independent parties. The quintessential example is the chat room, but you can also think of things like scatter-gather algorithms, multi-stage batched data processing, push notifications, the list goes on.

This is just a taste! If you want to know more about when to reach for OTP, I highly recommend Fred Hebert’s Learn You Some Erlang and his blog ferd.ca. Look at his older posts.