Verbal | SC regarding usage of Simple Present/Present Perfect

Hi Experts,
Need some help regarding usage of Simple Present/Present Perfect.
Although I have a knowledge what the above grammatically functions individually, most of the questions I was unable to crack not due to lack of the above concepts' knowledge but due to Context.
Within the short span of time I was inferring the meaning and facing lot of difficulty to arrive the correct thinking of author.
For example, some times Simple present and present perfect does not make much difference after all
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