We developed this as we needed it ourselves to interact with other networks as described in IC Side Services. We decided to release it as a standalone service to see if other devs find it useful.
A general use case is when you want to make a POST to an API that does not support idempotent requests. The alternative to using this service would be to deploy your own proxy between the IC and the API in order to de-duplicate the responses.
Also, there are use cases (like the “HTTP fire-and-forget”) in which it might make sense to trust an external service in exchange for a much cheaper and simpler way of sending requests.
I want to remark that this is not meant to substitute the IC-native HTTPS outcall feature as the trust assumptions are completely different. However, for the use cases mentioned above it might be a reasonable trade-off to make while the native feature improves.