God does not call us to serve by considering the "greatest good" that may or may not be pending or possible. He calls us heart by heart to serve the best we can by caring for the needs of others as we become aware of them.
From what position does God presume to "boss" how we use our time, money, energy, and reasoning? Colossians 1:16-17 explains God's position, as well as our own, very clearly and concisely: "By Him were all things created, that are in Heaven, and that are in Earth, visible and invisible, whether they be thrones, or dominations, or principalities, or powers: All things were created by Him and for Him. And He is above all things and by Him all things consist."
Furthermore, Jesus made a great sacrifice and paid a terrible price to redeem us of our sins. He wiped our sins away and promised eternal life for whosoever will love and trust Him. By all rights, shouldn't we always consider God's will and word before making decisions and choices?
Did you hear about the 3 little ladies who braved the elements to go Christmas shopping? "My, isn't it Windy?," the first lady said. "No Dear, this is Thursday," the second lady replied. "Me too," chimed the third lady, "Let's stop and have a cup of tea."