In formal academic essays or in IELTS task 2 essays. The Present Perfect can be used in two cases mainly, which are shown in the below examples:
Case 1) I have been married for 21 years.
The action "married" happened in the past, but the action is still happening now.
Case 2) When Australia has applied the economic policies which I mentioned earlier, according to the government statistics, most employees found a new job in supermarkets after their former employer companies had been closed.
The government applied these policies in the past, but I want to emphasis that these policies are still applied now. It is like "I have lost my book." Losing my book happened in the past, but by using present perfect, I want to emphasis that losing my book is still important now.
Two native English teachers said that the sentences in case 2 are wrong and suggested to use past tense instead, but when I discussed this with them they changed their mind. I wonder how native English speakers actually use present perfect despite what grammar books say as I want to learn avoid writing sentences which seem ungrammatical to most native English speakers.