There is no need to change the locks on your old home when you move out of it – the new owner should do this themselves. You should, however, change the locks on your new home when you move in – and this should be a priority!
You have no idea how many keys exist for the old locks, or to whom those keys belong. It is also a common practice for estate agents to put their copy of a key on a keyring marked with the address of the property.
It’s a small cost, but a huge benefit. If you moved into a new property and you were burgled by someone who used a key, your insurance company would not payout.
Furthermore, while you’re moving your belongings into your new property, it won’t be occupied at all times, though it will contain many of your valuables, conveniently boxed up and marked. Don’t be vulnerable – make it your priority when moving home.