FYI caffeine is a banned substance in NCAA and a lot of other organizations.
I can say when I was running track in college back in the late 80s and early 90s a lot of athletes were using caffeine and pseudoephedrine. I believe pseudoephedrine is now legal but it was banned back then. Caffeine was banned back then.
I am not sure of how much of a help caffeine would be to a baseball player. Its effect is more of a benefit to the endurance athlete. The line of thought is caffeine helps your body to more effectively utilize glycogen (muscle sugar). Pseudoephedrine would allow the body to more effectively utilize it oxygen intake. This would give the endurance athlete a boost when it came to using the bodies resources. That's why you would see the two combined.
There are some pretty serious side effects to using caffeine. First of all its a diuretic so you need to make sure you are sufficiently hydrated when using it. In addition you need to take it in higher dosages then you get from coffee or a coke and this can lead to nausea in a lot of people. In addition it tends to lead to more muscle cramping and tightness. Finally to use it properly you need to be caffeine free for 4 or 5 days before using it for performance enhancement which most people are not.
From experience (I am sad to admit) I will say that it can be a boost to the higher level endurance athlete (track, swimming, soccer(?)) but I don't think it would have much affect on a non-endurance athlete. Also its use as a performance enhancer is illegal and means you are cheating.