Design and Reverse Engineering

Reverse engineering can apply to many aspects of life. In design we use it to see how previous products were made, how they function and if there is any room for improvement. It's a process that can be used for electronic component, computer program, or biological, chemical, or organic matter) and analyzing its components and workings in detail. So what should I disassemble? My goal is to take a product and see all the components- like research and see what they do.