It is not wise to rely on handbrakes. Firstly handbrakes aren't designed to hold any significant load. Just search for an image of a handbrake cable. It is good

It is not wise to rely on handbrakes. Firstly handbrakes aren't designed to hold any significant load. Just search for an image of a handbrake cable. It is good enough most of the time, but it will bite you once you have a fully loaded car at a steep slope. Secondly it is a good habit to never leave the car on neutral unless you have a good reason because this habit will save you in the event of forgetting to pull the handbrake.