What will you do if you want to go out (walking) and you only have one key for the house and your husband has it currently? Simple as 1-2-3, let the house be duplicated! Or go out and ask your dear husband to get you afterwards. Not that easy, you have to tell him before you leave the house and let him get you when he's on his way going home, sounds better. Ha!
Since the landlord gives only one house key and it's okay to have it duplicated (of course! But make sure you have to take an extra care of it since that's a house key, that involves everything which includes your undies, oops! hehheh!), you then have to do so or else one cannot enter without the other and that is a trouble. That is how key duplication is important in your place. :-) For now, am still waiting for DH to duplicate the key at Home Depot store when he gets back at work for me (or for him). It's a hassle when we only have one key. Of course you cannot leave the house unlock! When you move-in, it's better to duplicate your house key for your spouse in the first day of stay. Remember that. :-) If not, we will find ourselves locked out and unhappy. Everyone maybe should just take locksmith courses!