According to the Merriam-Webster dictionary, a key is a means of gaining or preventing entrance, possession, or control. It is something that gives an explanation or identification or provides a solution, a usually metal instrument by which the bolt of a lock is turned.
No matter its form and material, a key is something we use to gain access to a place that is not normally open to everyone. A lock is there for a reason. Keys are a very important tool that shouldn't be in the possession of just anyone.
Why then is it important to keep multiple copies of the same key? A spare key, to be exact. The answer is the same for any reason we keep copies of one thing.
We keep copies of important documents to have one ready if the other suddenly goes missing. We keep downloads of important files in different flash drives to have a copy if our computer suddenly stops functioning. We keep multiple pens to have one we can use for different purposes or bring with us when we leave home. Similarly, keys are duplicated for safety.
If you're accidentally locked out of your home, maybe in the middle of the night after going out to a party, and you have no friend with a spare key that's currently awake, you have your own spare handy. It saves you precious time and money compared to needing to call a locksmith.
Sometimes, keys get worn out and old over time in ways we cannot notice because of us gradually getting used to the changes. Keys might suddenly snap out of nowhere, and how are you going to get home if you don't have a spare key?
If you have to go on a long trip away from home, it is important to have spare keys ready for your trusted friends and family. They can come in and check on your house for you, even water your plants, or take care of your pets if you have left any behind.
In the long run, having a spare key can save you money and effort as a home, car, and business owner. You can avoid keys that calling a Locksmith would need.
Communication is key.
While it is beneficial to have spare keys, it is dangerous when it's lost or given to a dangerous person. Be careful, and know the right things to do if you decide to have multiple spare keys.