Pros and Cons of Free Hosting

One advantage to free hosting is obviously the price. Note, if you're running some website that isn't initially supposed to get a lot of traffic, then what's the point of paying? In fact, it might even be possible to use your own domain on the free hosting which makes it even more attractive. Finally, if it turns out at some point you don't want ads or need more resources, then you can just upgrade.

Anyhow, can anyone see some downsides to this argument?