T3 app tRPC external calls

Currently i'm just making Post request and formatting my payload to

{
    "0": {
        "json": {
            ....data <--- actual data.
          }
        }
      }

{
    "0": {
        "json": {
            ....data <--- actual data.
          }
        }
      }

format. It works.
Saw that people use trpc-openapi for that. Is it really necessary? What are downsides of my approach?

T3 app tRPC external calls - tRPC