The device is protected with extra seals to prevent failures caused by dust, raindrops, and water splashes.
The focus motor moves the lens in order to autofocus. For system cameras, having a focus motor in the camera's body allows you to use a wide range of lenses, including lenses which do not have their own focus motor. For compact cameras, a focus motor is usually built-in.
We consider a lower weight better because lighter devices are more comfortable to carry. A lower weight is also an advantage for home appliances, as it makes transportation easier, and for many other types of products.
An optical viewfinder (or OVF) allows the photographer to compose a shot while seeing exactly what the lens will capture. OVFs have no time lag and require no power - as opposed to electronic viewfinders, which can drain battery life. OVFs are also better in low light situations.
A hot shoe can be used to attach an external flash, as well as light meters, viewfinders, rangefinders and other attachments.
A system camera has many interchangeable components such as lenses, flashes, and other accessories. System cameras offer greater flexibility than compact cameras.