With Kantu for Chrome webextension (HTML/DOM-based) the Selenium IDE selectFrame command is used to switch between the main page and the page inside the frames/iframe. For the visual Kantu automation, iframes are nothing special and no additional command is needed, except some little trick for scrolling.
Embedded Google Forms iFrame
iframes are often used for embedding content from other websites.
Embedded Youtube videos use iframes.
a9t9 tweets inside an iframe.