Let's say I wanted a good parking spot at the mall, so I go to the mall today and get the perfect spot. Then two weeks later I do the retro selection. Isn't this kind of pointless as what I wanted already happened. Would this not be just rehashing some already fulfilled desire. Not to seem negative but this just doesn't seem worth it. If it's already happened then you not doing it at a future time will not cause some world ending paradox. It seem like "I had a pepsi yesterday but I want one today" "I guess I'll think about how good it would be to have a pepsi yesterday." The only thing I can see working like this is altering a memory of the past to make yourself think you did something that you didn't. Correct me if I'm wrong.
If the question is why bother, then I'd like you to picture a situation for me. You've been up all night, so you are tired. You are waiting, early in the morning, for some big project or final to start. You want it to be smooth sailing, but you can't focus due to your fatigue, and there is simply not enough time to meditate to gain the proper focus needed to perform the future selection. You've only got a minute. Which, as it so happens, is enough time to formulate a plan to perform a retro selection to ensure that the final is going to be easy and smooth sailing.
In short, the point of this is to be able to perform all of this cool psi stuff, when there is not enough time at the moment to do so right now. And yes, that example is something I've encountered before (Physics finals can really suck sometimes...)
However, there is another point you've made, which needs addressing, and I'm glad you brought it up. There is a question which looms over this article, namely:How can we be sure that this is due to our influence, and not just something that would have happened anyway?
First of all, let's apply your example of the parking spot at the mall to a normal future selection situation. First, let's say that you want a good parking spot at the mall, so you go ahead and do a future selection before you leave to go. Then, hey, you get there, and someone is leaving just as you drive by your favourite store, right there in the front. Cool. But here is the question: how did you know that it is your influence? It might have just happened anyway, with no relationship with your psi performance.
How do we know that any of this works? Well, there are two options: We can either use it to make something really hard to deny happen (This is stuff like the psiwheel), or we can keep performing future selections on everyday things like your parking lot example, and note if it works most of the time or not.
So, repetition and consistency are what we are looking for to prove that a psionic effect is happening. This is good, because that's how we do science, incidentally (Remind me to write an article telling everyone that science and psi are not enemies, one day).
Therefore, to prove that this is happening, we have to do this repeatedly. Isolated incidences like the example you gave ARE of suspect. If you did it once, and this happened, I would be suspect. If you could, say, write a note to yourself for later, and the thing you wrote to yourself happened almost all the time, then I'd be inclined to believe you. I can say that this is how I confirmed that it works.
But, let's say that you wrote a note to yourself to get a good parking space, and then forgot to perform the selection, yet still got the space anyway. Well, is it difficult to believe the non-retroselection situation, where you could have performed a future selection before you left, forgot to do so because you got interrupted by a phone call or something, and still got the space? This is just a coincidence. You can't rely on coincidences to happen each time. No psionic action happened.
However, with proper practice, performing a psionic action would almost guarantee a situation happening. That's what this is all about: guarantees.