Counting cards is actually used in blackjack. We can say we count cards in poker but it is more counting the stats.
For exemple if i know the cards you hold i can decide i will put all my chips in with the worst hand if i get the correct % to win money in the long run. For exemple im holding 2 spades on a board with 2 spades....i get arround 37% chances to get a flush and win so i would usually fold against one player but i might call against 3+ opponent because i will be winning more then losing in the long run