The idea of web 3.0 and the ethereum/ipfs structure is that you have a fat client and thin server. This means that all the business logic sits on the client and the server is just utility.
Filecoin and the ifps structure allows content like text or images to be stored in a place that the smart contract based client could access.
Some recent examples are:
- Marketplace that uses ifps to store data: https://demo.originprotocol.com
- Game (not sure if this uses ifps) http://cryptokitties.co
Filecoin eliminates a lot of the overhead of selling storage, but it adds some overhead all its own. The big question is: which is larger, and by how much?
That said, I'm not familiar with it in-depth, and I'd love to hear otherwise if someone knows!