Statistics of your own game. Such information is needed to analyze and evaluate your own game, to identify strengths and weaknesses. In addition, with the help of special programs, you can find out why you still lost in the last game (search and analysis of leads), and won in the penultimate game with the same set.
Opponent statistics. If you know enough about the enemy, then you do not need to worry about the outcome of the battle. It is not for nothing that spies remain one of the most demanded professions (or is this a vocation?). Various services provide information about the opponent, such as the number of losses / wins in a certain period of time, play style, time at the table, bets, etc. You do not need to be seven inches in your forehead to understand that if a poker player is leading himself aggressively at the moment in this game (and statistics show the opposite situation and a low percentage of aggression), then, most likely, he has a strong hand, and you need to quickly figure out what to do. Don't save statistics.
By the way, please note that absolutely every player can collect statistics, and in the general database, since you can find the necessary information about your opponent, they can just as easily find it about you. It is important to remember this during the game itself in order to analyze game situations.