Have you ever watched rust overtake a metal object? Watching a time-lapse video of it can be pretty interesting, but when you see it happening to something that you own, it might not be as fascinating. You might be surprised at how much of your home is prone to rust. Of course, there are methods employed to prevent this as much as possible, but if rust takes hold, it can spread and do damage quite quickly.
While some of it might just be cosmetical, such as brown streaks from rusting nails, there are some situations in which rust can have a very serious effect. For example, if the rebar inside of cement starts rusting for some reason, it could affect the structural integrity of that cement, which would be very bad if it was part of your foundation. If you have a metal roof and it starts rusting, you could soon experience leaks, leading to water damage.