In LTE, out of all events I heard A3 event is most important . Why?

Question

If I am wrong, please specify which event is important?

Answer 1

All events are important. A3 event is used to trigger intra or inter freq HO. As per A3 event definition:
The LTE Event A3 is triggered when a neighbouring cell becomes better than the serving cell by an offset. The offset can be either positive or negative.