It's certainly more practical than trusting other people's opinions and spending $50 on a game I may not even like.
What gives you the right to take a copy and then not buy it? If you think that playing a game for some amount of time that is pirated and then not buying it is simply trying it, then I ask: at what point does it go from a trial to a case of piracy? An hour? Two hours? Four? 25% of game completion? If you pirate something and don't beat it, is it still piracy?
If you do buy your games and do use piracy as a tool for meriting purchases, than kudos I guess. All I know is just about everyone uses that excuse and I think fairly few actually bother to go out and buy it.