I recently wrote about when dApps are appropriate. In that post, I made the distinction between 1:n and n:n apps. 1:n is any app that is designed for creators serving their own audience. In reality, there's more than one creator, so this is in fact just a type of n:n app.
The difference is the ratio. Creators on YouTube, sellers on Amazon, and any other kinds of creator are trying to maximize their reach. They want a large, loyal following. Typically, this is because of some financial incentive. The app they're creating for has enabled their business to reach more people than if they were not using the platform.
Social networks like Facebook on the other hand don't incentivize large followings. It's just a place to connect. You're on a level playing field with all the other network participants. Sure, you can be more popular, but you don't gain anything tangible for that effort (unless you're selling something elsewhere... then you're just trying to convert your Facebook followers into customers).
So, here's another way to determine whether your app should be a dApp:
- Private - this encompasses "solo" and "1:1" apps from the previous post. If your users don't want their data available for the world to see, don't store it on chain.
- Permissioned - apps like Patreon and OnlyFans. If content is gated behind a pay wall/membership, this is a good opportunity to use blockchain. You can use NFTs to grant access. The content itself may or may not be on chain. Depends on the app.
- Public - If the data involved in your app isn't private in any way, blockchain is appropriate.
Again, different features of your app will often cross these lines. You'll probably have a bit of everything.
P.S. Also consider what your users will want monetized. Not everything should have a financial incentive.