In the scenes, the « send a message » action allows you to use the value retrieved from a sensor. It would be convenient to be able to do the same in the « make an HTTP request » action (in the ‹ body › field).
For example, this would allow you to send the value of a temperature sensor to your chosen server via HTTP. At my place, I have an HTTP server that converts what it receives into an audio file (with Google’s text-to-speech) and then makes it audible in the house.