1. для действий в прошлом, связанных с настоящим моментом.
e.g. He's lost all his money and now feels utterly desperate.

2. для недавно совершённых действий
e.g. I've lost my keys! (I remember putting them in my bag this morning but know they are not there now.)

3. для действий, начавшихся в прошлом и продолжающихся в настоящий момент (альтернатива Present Perfect Continuous).
e.g. She has worked as an accountant for 10 years. She's a really experienced one now.