What advantage to you gain by testing with Appium?

I don't understand why I should choose appium for UI testing. The only real benefit I see is that it allows me to write tests in whatever language i'm comfortable with. But say I have an Android application that i want to test. Adding Appium as a way to UI test just seem to have overhead by having a HTTP client/server. Instead I can just use Espresso and write the test that way. This reduces the time it takes to run the tests since I don't need the Appium server/client. So should I only consider Appium if I want to test my app cross platform? But even then it seems more efficient to write iOS tests in Earl Grey and Android tests in Espresso