I flew standby once about 10 years ago and it worked beautifully. I took an earlier flight in the same day as the one I had bought the ticket for. I wouldn't assume it would work as well today. Airlines are trying to find ways to squeeze more money out of passengers. My wife asked about it recently and was told there would be a $50 fee for changing. I still think there might be a way to make it work without the fee, though.
There might be times when it would be worth it, even with the fee. Say you needed to go somewhere in a hurry. Buying a ticket today for a flight today would cost a fortune. But if you bought it for 2 weeks in the future and then flew standby today, I think you'd save a lot, even with the $50 fee.