Why is it better to use original nano sim card than cut your normal sim to be nano?

Because original nano sim card is 4g coverage

1. Frequent coverage loss.
2. Reduced coverage (signal strength).
3. No 4G while they were in an area covered with 4G. After the SIM swap, 4G magically appeared:)
4. Call drops.
5. Slow internet due to instable connection.
6. Battery drain due to frequent network searches.

The  thickness of normal SIM is higher when compared to nano SIM, about 15%   Secondly it is not advisable to alter the SIM provided by the service provider.  When a normal sim is cut, always scope for damage.