In many cases the units of measure are dollars and cents because these represent numbers which can be compared objectively. Both appear to be sound investments, but the first will return more net benefits than the second. It is nice to evaluate in dollars, but this is not always possible. There are many benefits such as personal satisfaction and employee incentive which cannot be evaluated in dollars but do weigh heavily as benefits in many decisions. Timing Production of benefits early rather than late is a concept which is forgotten all too often.
Benefits usually have a pleasant way of compounding over time.
In dollars, this is the time value of money. Obviously you want them today. Money is most valuable to you right now because you can reinvest it. Risk Making investments which are safe rather than risky is often difficult to do. Evaluating risk can be extremely complicated, especially when you want to compare the risks involved in alternative investments.