Photon Unity Networking PHOTON_DEVELOP directive

what does the #if PHOTON_DEVELOP directive shown below do?

#if PHOTON_DEVELOP
            if( ReceivingSender != null )
            {
                ReceivingSender.OnPhotonSerializeView( stream, info );
            }
            else
#endif
            {
                if (stream.PeekNext() is byte[])
                {
                    this.DeserializeSynchronizationTypeState(stream);
                }

                this.m_StreamQueue.Deserialize(stream);
                this.DeserializeDataDiscretly(stream);
            }

It’s a compile define we use to develop/debug some cases.