Tracking programs are helpful in better and more fully analyzing your opponnent's play. Programs such as Poker Tracker, or HEM catalog all your hand histories, saving vital stats that allow you to critically and objectively break down your own play, allowing for improvements to your game.
Further, information deemed advantageous about your opponents can be displayed on top of the tables you are playing at, allowing you to see their Vp$ip, Preflop Raise%, and Agression Factor, among other things.
The use of this information can aid in making better decisions, and that's always a good thing.
While you cannot use this software when playing live, you can still perform similar types of analyses, simply through observation and some mental math, and the principles that allow you to use tracking software to make better plays online do transfer to the felt.