From Envirowiki

Cost benefit analysis (CBA) is a tool for measuring the value of an action by comparing its potential benefits with its costs and risk. However, CBA is inherently limited to those parts of society and the environment which can be of direct economic benefit (since benefit is measured in financial terms). This makes CBA useless when discussing non-financial benefits/cost, such as the extinction of individual species within ecosystems, and mental and physical health issues. Some of these impacts are extremely important, and cannot ever be adequately quantifiable due to the large number of unknowns, even where they have some quantifiable outcomes. How can we place a dollar value on the trauma and dismay experienced by the population of the Cartaret Islands, who are now being forced to flee their submerging homeland? There are many species which have no commercial value whatsoever to human societies, but does that mean we may let them go extinct? CBA discounts such unquantifiable impacts, and therefore is extremely limited. It can be a useful tool in some circumstances, but should be used in conjunction with the Precautionary Principle.