Actually i use many software, for tracking and analyzing my game or even a game played by someone. (For example to see exact
odds of some
hands played not by me.)
PT4 - because it's best tracker in my opinion. Helps me a lot at many points: shows me exact BB amount in stack of everyone, releasing me of that time-consuming task calculating in mind every time every stack i need to transfer to BBs. Also shows a lot of other useful stats like VPIP, PFR, LIMP frequency, Steal frequency, pre-flop 3bets etc. Also a really powerful tool to make notes, tag hands & replay them. I tell you, once you saw replay running by PT4, you will be laughing about any built-in replayer at any poker room. It also shows me a lot of useful statistical info about my own play, at which type game or specific situations or even with which hands i win or loose most. So i can study and improve my game much more target-oriented. If it's still not enough, it also collects all hands from all my poker rooms and make back-ups nicely. So i will never loose my hand history and have it well organized. And even provides a nice hand converter for the forum (to post for hand analyze), so it looks much more reader-friendly and releases from looking the hand through handhistory.txt files, where hundreds of hands usually are.
But of course i use also some other software for analyzing, such as ICM Trainer, Equilab and PioViewer. I have heard Flopzilla shall be nice too, but i havn't bought it yet.
Honestly, you shall use any possibility to improve your game and software is a great help. I think that the most people who write they don't need any soft, because they use their brain, simply didn't use any or didn't sorted through. I mean of course all you need is a bright mind to be a good player, but a software can help your mind a lot.
But well, it's a matter of taste after all.