Why does Mighty need a WiFi connection to sync?

WiFi is used to sync your tracks to Mighty as quickly as possible. Mighty cannot sync over a cellular connection at this time, but you can turn your phone into a WiFi hotspot and use that network to sync.

Note: If you're an iPhone user there's a known limitation where you need to connect another device (like a laptop) to the hotspot in order for the network to show up in the Mighty app.