If you have bought the latest iPhone, you need to get a protective case for it as soon as possible. The best time to get one would probably be when you buy your iPhone, but be wary not to get ripped off as many shops grossly overcharge for iPhone cases.
Without cases, you are running a high risk of damaging your iPhone, and potentially having to pay large bills to have it fixed. You can buy iPhone 7 cases via https://tradearmour.com.au/collections/iphone-7.
The construction of the iPhone is very good, and the aluminum is very strong, but the glass panels on either side of the phone are very vulnerable to scratches and breakages. To put into perspective how much repairs can cost, for a replacement screen you are looking at paying over 200 dollars.
An iPhone case is a relatively insignificant investment compared to the price of purchasing a new iPhone. What I find is that people don't realize how easy it is to break their iPhone, they seem to forget just how delicate and intricate the inside of an iPhone is, and that the glass covers are very brittle. Simple things like leaving your phone on the edge of the table, one slip and you could be looking at over 200 dollars of damage.
A misconception is that an iPhone case is expensive, from online auction sites you can buy a case for as little as a dollar. All you need to protect your iPhone is a leather sleeve or a simple plastic case. The case you need to buy must be cushioning and be able to absorb some of the shocks, should you drop it.