Okay, so it seems that Skills are for 3rd party apps and devices to be able to interface with Alexa devices. Keep in mind that the Skills are developed by the 3rd parties who developed the apps and/or devices. Therefore Skills can be flaky. My TP-Link skill for example does not properly send Scenes created in its Kasa app to the Alexa app, and so Scenes cannot be used with their device via Alexa. The Scenes work fine using their Kasa app though.