Why was APPEND_IF_FITS deprecated?

I could not find documentation on why the atomic operation type APPEND_IF_FITS was seemingly deprecated - it’s missing in the 7.1. C API documentation and marked as deprecated in the Java bindings (MutationType (FoundationDB Java Client API)).

Can anybody shed any light on this?

I would have liked to use it to encode sparse multisets without reading prior values, what are the data modelling choices without it?