If you see the same players over and over, you can be fairly certain the odds
are they are using a tracker and have numbers on you. In which case a Tracker/HUD will only be a neutralizer if you use it right.
If, on the other hand, you never see the same people twice, then the Tracker will be helpful in self analysis.
Everyone will agree that the more hands you have on any player, the better. I also agree, however, I often cut down the number of hands showing for players to today's hand count. This gives me a notion of how they are playing today, now, without the garbage of how they played last year. This is usefull in tourneys, where I may know some or even many of the players, but will not know many at all, so I get a feel for how each is playing this particular tourney. It is info I would not have without crazy note taking for each game.
So, if you can agree that if you knew everything about a hand of poker, and in the extreme that would mean you knew villains cards, then you will have to agree that having more info at your fingertips, can not be a bad thing.