When talking of upwind tactics lee bowing the tide is a phrase that pops up fairly often but is equally often not fully understood. When beating upwind and across any tidal streams, there are real advantages to be had for setting a course that puts the tide on the leeward side. The benefits are best demonstrated graphically:

Two identical boats start at the same point, with the intention of beating directly upwind to the same destination. There’s a strong tidal stream coming in from the right.
Boat A decides to start on starboard tack (meaning the wind comes in from the starboard side). Boat B chooses port tack. Hard on the wind, they both make the same speed through the water.
Now look where they both are some time later. With the tide aft of her beam (a ‘fair tide’) Boat A is carried a considerable distance from her departure point. In the meantime Boat B, has been partially balked by the tide which is forward of her beam (a ‘foul tide’). Both boats have made the same progress to windward but Boat B is significantly nearer its destination

For more on tides see Rule of Twelfths