Sound travels about one foot per millisecond. Even if output from the speakers is perfectly time aligned, when the listener is standing near the speakers in one room, the other room is "late".

This is not always a problem. In an outdoor restaurant setting we used a Sonos CONNECT to add sound from a sound stage to the house system. Since there is about a 70ms latency between a CONNECT Line-In and output from another Sonos Player, this latency is normally a disaster in a live music system. However, in this case the stage was 70 feet from the house speakers and the listeners. The alignment was perfect.