HREFLang allows you to tell search engines which language and country that a particular page is best suited for.
Shouldn’t Google figure this out on their own?
Generally, yes, they do. But Google isn’t perfect and there are times when it’s more complex than you may think. For example, a page of English language text could be relevant for someone in Australia, New Zealand, Canada, the United States, or the United Kingdom. HREFLang tags let you tell Google exactly what location a page targets.
Even non-English speaking countries can be confusing to Google such as parts of Canada who speak French and the clever people of Switzerland (hey JohnMu!) who speak English, German, French and Italian.
Customers need to land on the right page
HREFLang tags help search engines display the right page at the right time in their search results. If a potential customer accienallya lands on a French version of your product page rather than the English version, they may not bother looking for the right one and may instead bounce straight back to the search results and go elsewhere.
Losing customers = losing money.
You can’t always see when a HREFLang tag is wrong
The problem with HREFLang tags is that the little things are hidden away in the HTML of your page which means that looking at the front end of the page won’t show you that something is broken.
Not to mention that even if you do look at the HTML, a single wrong letter here or there is hard to spot and could mean that Google makes a mistake and before you know it, you’re targeting people in Nepal instead of the Netherlands.