This is a reverb device that works with "impulse-responses". Impulse-responses are generated by recording short broadband signals and their corresponding room-reflections. What you get contains the information needed to reproduce the same room with other signals.
Due to technical reasons the plugIn works with a fixed latency of 8960 samples that is compensated for by the VST-host.
Sir is a stereo plugin. To take full advantage of stereo impulses for mono signals, you must first convert the track to stereo.