Its unlikely that any two players would ever pick precisely the same combination of troops. Most players start by buying a few models and painting them without worrying too much about points values or what they are. This gives you a flavor of the army, and by adding sufficient models to make a regiment, enough to play a modest game. By adding more regiments, as well as war machines, heroes, wizards-and other special models you army will soon grow bigger. If you have more troops than you need for a battle, this gives you the opportunity to 'tailor your force to suit your opponent.
Some troops are particularly effective against others.
The High Elf repeater bolt thrower is great at cutting down enemies who attack in large regiments such as Skaven and Goblins, for example. Core units' are the standard infantry or cavalry that every army has in abundance - Ore Warriors, High Elf spearmen and archers, Skaven Clanrats, etc. Although you don't have to play Warhammer with painted models, there's nothing to match the sight of two painted armies facing each other on the tabletop. Some people paint their models quite simply so they can start gaming straight away, while for others painting miniatures becomes a satisfying pastime in itself. Most gamers, though, fall between these two extremes, and paint models to a standard they feel comfortable with, but which allows them to finish their armies relatively quickly.