It is a disruption that is too difficult to be useful. It could be counter productive because it diverts attention from other important details.
It is often obvious when one of your opponents is about to do something. You can infer what cards players have based on the trades they offer, and their reactions to dice rolls. Observing your opponents yields more valuable information than attempting to memorise their cards.
I do track cards when there is a rare resource or a player is about to win. A player with eight points on the board and two army cards, for example. The player may need one ore to buy what could be a third army card, so it's worth keeping track of cards.
I do count development cards. It is easy to tell what development cards other players have. There are five victory point cards, for example, and usually players hold on to them for much of the game.
You can gather information using deduction: Given the development cards you have, ones that have been played, and how many remain, you can make high fidelity guesses and estimate the probability of pulling out a card you need.
Recently two development cards remained in the game and I knew that both were victory point cards, which allowed me to win the game.