When referring to a sailing boats course relative to the wind there are some clearly defined terms like "beam-reach", which is exactly perpendicular to the wind. A broader range like "close-reach" is defined as between "beam-reach" and "clause-hauled". The latter is what I am not so sure about. Wikipedia defines it as

> the craft's course is as close to the wind as allows the sail(s) to generate maximum lift.

That seems to make sense in terms of optimizing speed: If you go more leeward the boat with the tightly trimmed sails will capsize and if you go farther windward you'll get slower.  
All texts I read mention "clause-hauled" as the "normal" direction when sailing upwind (not explicitly, it's just always the term used). However if your final goal is directly upwind, speed when sailing "clause-hauled" competes with a direction closer to your final goal when pointing more windward.

What I would like to know is what exactly is the significance of sailing "clause-hauled"? Is it always (well mostly) the ideal course when sailing upwind?