Like Denny says, play around, experiment, and learn for yourself what it does.
Lately I have been splitting every batch of beer I make, using two different yeasts, then comparing results. Inevitably, half the batch turns out excellent, and the other batch mediocre. If I continue in this fashion, half my beer will always suck, half might be quite good, and eventually, I'll know what to do.
There's only so much reading we can do regarding yeast. They are living creatures, always evolving, and somewhat finicky. The best way to learn is to use them, try different strains, try different temperatures, try different pitching rates, try liquid vs. dry packets........ and keep on playing until we find what we need to do to produce the beer that WE like to drink.