Here are a few reasons why you would need a key programming or replacement done:
1) When the battery on the remote dies.
2) If you drop the key in water or a similar it can become useless (hence reprogramming a spare key).
3) children pressing buttons or in your pocket, the remote won’t open the central locking on most occasions.
Diagnosing a vehicle is complicated with the ever growing technology with Immobiliser, DPF, BCM and many more complicated electronic and electrical parts in everyday cars! Be sure to use the right garage with the right technology behind the right technician!