Benefit, profit, avail mean to do good or to be of advantage to someone.
Benefit usually implies personal betterment or improvement (as of one’s physical, intellectual, moral, or spiritual condition), but it may suggest enrichment or a furtherance of one’s ends.
Profit carries a strong implication of gain, especially material gain. It is therefore preferred to benefit when an increase or yield, as opposed to a decrease or loss, in one’s store (as of wealth, power, or knowledge) is to be suggested; thus, he always profits (not benefits, unless one wishes to imply a salutary effect) by the misfortunes of others; no one benefits from a war except those who seek to profit by it.
Avail, which has an archaic and literary flavor that makes it rare in speech except in historical novels or in sermons or orations, stresses efficacy.