Was talking with some engineers the other day and the question came up of the differences between Invoke-RestMethod vs Invoke-WebRequest and which cmdlet to use when. Some detailed information from Billy York, but the short answer is:
REST for well-formed objects, WebRequest for html.
Specifically Rest-Method is intended for REST endpoints (JSON, XLM, etc.) and can consume the properties and methods (if available) on those endpoints, where as Web method is better suited for HTML static pages.
Hope that helps clarify the options for you when working with web page content.