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.
A hot shoe can be used to attach an external flash, as well as light meters, viewfinders, rangefinders and other attachments.
A higher screen resolution provides a sharper image, making it easier to review your photos.
A system camera has many interchangeable components such as lenses, flashes, and other accessories. System cameras offer greater flexibility than compact cameras.
A flash is good for low-light environments, and can sometimes be used as flashlight.
The bigger the screen size is, the better the user experience.