Think of it as if HIVE being the internet, and INLEO is one website on the internet. Being on INLEO means you are on HIVE, but being on HIVE does not mean you are on INLEO.
Most of HIVE Applications require Posting/Active Keys to work, and the Keychain App helps you provide the keys to these applications securely. One big example is Hive-engine, the platform that you can trade LEO on with other HIVE Tokens: https://hive-engine.com/trade/LEO