The 0.37 you get back is the tax you paid on the income. The exercise is more about controlling where your money goes and what it goes to.

Instead of giving the money to the government, who you may not agree with, you're giving it to a cause that either directly or indirectly can benefit you, whether that cause is a direct benefit in the form of helping with a problem that is causing you trouble, or simply as a good PR move.

You spend money to get there, but now often than not you're getting a benefit from the transaction.

Billionaires and their mentality and interests are fairly well known, for the most part. Bill is a co-chair of the foundation and likely recieves many benefits from holding that position, including a salary. He can also, as chair, influence who is hired, providing stable employment for people who are in his favor, while also getting a massive boost to his public image, all while paying himself a salary. He can also direct the funds that would normally go to the government as tax, who may spend it on things he doesn't want to happen, and redirect those funds to something he would like to see happen, such as R&D into technologies (which is a nontrivial part of what the foundation funds).

For Bill, the charitable foundation is a win all the way around, except to his billion dollar bank account, which I'm certain is providing plenty of income on its own.

Quite literally he's taking money out of the hands of the government and making sure money is being funneled into things that he thinks should happen. It looks very selfless on the surface but gates is a business man, this is just his most recent endeavor.