The purpose of prayer should not be primarily to obtain gifts from our heavenly Father;  it should be our intention to bring us into personal contact with Him. Prayer is simply talking to God. Some have asked why is it necessary to pray when surely God knows all about us before we even pray. It is true that God knows before we pray, but prayer is important for us - it allows to articulate what is inside of us - much is revealed to ourselves when we pray.

In my opinion, if a person prays for physical world outcomes, our prayers may or may not be answered. According to Emanuel Swedenborg, our eternal, spiritual lives are what are important to God. God, who can see from the beginning to the end, wants each individual to be in Heaven where there is eternal happiness and bliss. Sometimes, if we were to get our physical wants and cravings met here, we would do harm to our spiritual selves, so God puts the emphasis on our eternal lives. I have often heard it said that God takes care of our needs - it's our insatiable wants that He disregards. He knows our deepest needs - our good and true longings of our heart better than we do ourselves - and those do make a difference to God. Whatever happens to us in this world, it is but a temporary condition and God does take care of those who look to Him for answers. 

So always pray for the spiritual good of a person -
knowing that God does indeed know better than we do. 
"Lord, Your will, not mine."

Here's a link for a scientific study into whether prayer works!
  Archives of Internal Medicine