Why does Hashem need our prayers?

Why does the Creator of the universe need my prayers, if He does not need anything? It is only my interest to pray in order to get what I want, but why does He need it? What is the meaning of it for Him?

Dear …!
That’s a great question!
The Creator, Blessed be He, created a perfect world for us in order to do us good; with His infinite wisdom, He knew it would be best for us to receive the flow of His kindness only through prayer. To understand the concept, we can imagine a loving father who, in order to educate his son, only wishes to give him after he asks. However, in his heart of hearts, he dreams and hopes for his son's requests. In fact, the father’s desire to give is much greater that the son’s desire to receive.
There is an additional point here, though. When a person prays, he connects to the Creator and becomes a better person, reaching a higher spiritual level. Therefore, before the prayer, the things that he wanted were not necessarily good for him; after the prayer, he is on a different level and sometimes receiving the flow will now be good for him.

Maharl (Rabi Yehudah Loeb of Prague), Beer Ha-Gola (the Fourth Well, chapter 2)