hreflang is an annotation that helps Google understand that several URLs are alternate language or regional versions of substantially equivalent content. It is useful when an independent consultant has pages written for different Spanish-speaking audiences, but it does not make a page more relevant, more authoritative, or more likely to rank by itself.
For a consultant, the important decision is whether separate versions are genuinely needed. A page written for Spain may use different terminology, examples, commercial references, or buyer expectations from a page written for Mexico or for Spanish-speaking prospects in the United States. If those differences are meaningful, hreflang can help connect the alternatives.
Common Spanish variants include language-region combinations such as es-ES, es-MX, es-AR, and es-US. The code should describe the actual page audience. Do not create regional variants merely to cover more markets if the content and service proposition remain identical.
A correct implementation should point each alternate page to the other valid alternatives and include the page itself. The referenced URLs must resolve, be indexable when intended for search, and contain the language or regional content promised by the annotation.
The key point is separation of responsibilities: localization makes the page useful to the intended audience; hreflang helps Google understand the relationship among alternate versions. It should not be described as a cure for duplicate content, cannibalization, weak localization, or poor site architecture.