This tutorial provides insights into some important do's and don't of robust PCB Design
Design rules are there to help you. They represent the bare minimum of what a manufacturer knows to work. A big warning here: Just because the design rule test passes, doesn't mean your design is robust, it simply states that when it fails it is guaranteed to fail during manufacturing. Click here to find our design rules here
A whole copper plate is included in the base material. During the manufacturing process this is etched away. Even though the etching machines are extremely precise, thin copper traces means a lot of the stuff around them needs to be etched away. This is a very risky process the longer the trace becomes. Hence try to keep thin traces as short a distances as possible.
Basically the same applies to trace distances for the same reason. If the space between them is to small, it is like a negative copper trace. This means chances are not every detail is etched away and hence short circuited. Hence try to avoid having too little space between traces longer distances.
Remember copper is free. Every copper that you keep does not need to be etched away and hence poses less risk of causing any unwanted short circuits.