At least for me, I don't really care when I'm behind in the count. And for professional hitters, they should be able to know how to fight when they're down 0-2, 1-2, etc... The first pitch for me in that situation lets me know what I'm up against. It's usually a fastball, so I let it go by to see if I'm able to catch up with it. If it's too fast or overpowering, and I swing at it, not knowing I can't handle it, I'll screw something up. If I know I can't handle it, I'll foul it off until I get something better. Same idea goes for any pitch.