Should we believe the theory of evolution because it is true, or should we believe it because believing it helps others?
Um, that's conflating factual knowledge with living one's beliefs.
Suppose someone is very sick, and can only lay down in bed. And he is praying. So "his faith is of no benefit to others (in deeds)"; just a burden (money wise).
Money is only a very very tiny thing here. Deeds are not big things. They can be very apparently tiny things like saying "thank you" to people when they've done something pleasant or helpful for you.
If someone is earnest about one's beliefs, people can find endless opportunities to try to live one's ideals.
'Always preach the Gospel, when necessary use words.'
Saint Francis of Assisi. While his life and deeds were of his time and place, the essence of the life he lived still inspires people today.