Every conservation agency handles more threatened species than it can fund. Deciding which receive effort is unavoidable, and doing it explicitly rather than by default is what triage means.
Why the choice cannot be avoided
Budgets are fixed while the list of species requiring action grows, so any allocation implicitly deprioritises something whether or not anyone says so.
Implicit decisions tend to follow attention, funding streams and institutional habit, which produces an allocation nobody designed and nobody can defend.
Making the criteria explicit at least allows them to be argued about, which is the practical case for the approach rather than a claim that the choices are comfortable.
What the ranking uses
Most frameworks combine the cost of an intervention, the probability it succeeds, and the benefit if it does, which usually means expected persistence of the species.
Cost matters more than it initially seems. A cheap action for several species can outperform an expensive action for one, even when the single species is more threatened.
Probability of success separates species with a known, workable intervention from those where the threat is not understood or lies outside the agency's control.
Where distinctiveness enters
Some schemes weight species by how evolutionarily isolated they are, on the reasoning that losing the only member of an ancient lineage removes more unique biology than losing one of many close relatives.
This favours unusual animals such as tuataras, monotremes and certain amphibian families, which otherwise attract little attention.
It also introduces a value judgement, since it holds that not all species are equally worth saving, which is precisely the claim critics of triage object to.
The main objections
The strongest criticism is that triage accepts the budget as fixed, when the budget is a political choice rather than a natural constraint.
Publicly labelling a species as unfunded may also become self-fulfilling, discouraging the private donors and volunteers who might have supported it independently.
There is a further practical concern that models depend on estimates of cost and success probability which are frequently guesses, so the arithmetic can convey more confidence than the inputs justify.
How it is applied in practice
Most agencies use ranking to inform decisions rather than to determine them, retaining discretion for species with legal obligations or strong public attachment.
Frameworks are also used to argue for more funding, by showing precisely which species a given increase would move from unfunded to secured.
Used that way the exercise functions as a budgeting tool rather than an abandonment list, which is how its designers generally intended it.