More than recommended it is required to use this call signature. The observed data doesn’t change with every draw, not sure what you mean with the conversion thing, why does having the observed data be the input in observed kwarg make a difference on this?
Technically you could have a value argument that is ignored, the restriction is on that being on the call signature, not on using the value argument. If you then want to ignore it and embed the data there that is on you, and if you do I’d double check all the results to make sure nothing is not behaving as expected.