I apologize if this is a chicken-and-egg type question, but are lefty hitters or lefty pitchers more valuable to a team?

I understand the platoon advantage and that left-handedness is an advantage in sports because of its rarity.

But in baseball, are teams more focused on lefty batters to combat the opposing team's righty pitchers first, and then they go looking for lefty pitchers to get an advantage over the opposing team's lefty batters? Or is it the opposite?