Ok. It does a few things. First and strangest, I owe something to the person I am lusting after because lusting is always an act of "taking". I am using their image for selfish ends. (And saying that "They are obviously begging for it cuz look at how they are dressed!" is BS. I am reasonably certain that the average slutty female out there intends to be lusted after by who they want to be lusted after, not by some compulsive, perverted Jew boy like me.) So how better to show my gratitude?
Second, lusting is the single most powerful, portable, and dependable way I exercise my MEEEEE muscle (the one in my head, not somewhere else). It is my drug of choice for entertaining myself, for covering up stress, fear, and boredom, for controlling my inner environment - in short, it is my most trusted Power source. Otherwise, why would I use it so much? So how do I sacrifice it? By just saying "no"? Nu. OK. That's what I always tried to do.. it didn't get me very far away from it. If you know anything about operand conditioning or habits, then you know that I choose to go a step further and use my lust as a guide and tool for giving power to others. To helping me learn to care about helping others. What better way to weaken the MEEEEE muscle than to do what little I can to care about the very people I naturally worship as my (false) Power Source? I turn the tables as much as I can.
Finally, it gives me something to focus on rather than on lusting. And that itself is worth everything, even if my prayers for her are of no benefit to her. Treating a lust object like the real, live person they are is one of the most powerful tools to help me to stop looking at them like pieces of meat (with skin on them). We need to be reoriented. The entertainment and porn industries have succeeded in getting so many of us to believe deep in our hearts that pretty women are all dolls; that above all else they are libidos desperate to be used by us; and that they don't have real lives with obligations, pains, joys, sadness, and dreams of real people... and that perspective entitles us in our hearts to treat them as objects. Is it any wonder then, that most lust addicts grow to expect (no, demand) sexual bliss from their wives as though their feelings are just an obstacle? I looked into the shulchan aruch to see what I could demand of my wife, rather than looking into her heart... now what kind of BS is that? No wonder we were so miserable back then! She was an object, in some respect.
We need exercises to change, it will not happen just because we wish it to. And it takes a long, long time. But it works and it is worth it.
A caveat: I was once walking with an SA beginner who was staring at the rear end of a lady out in front of us, and mumbling. I asked him what the heck he was doing. He told me that he was praying for her.... I reminded him that he might be praying for her butt, but not for her. Ha. We both had a laugh went on our way. So the praying can't be done as an excuse to keep staring! A sweet dufus, he was.