Why? Connector pins only can carry limited current.
Why? It compares components between more manufacturers and shows a lot of important information.
Why? It’s much more comfortable during HW design. You can open Schematic in one monitor and PCB in the second.
Why? It may be difficult to route the interface and do length matching. You may need space between the memory chips and between CPU & Memory chip.
Why? Big gap / clearance between tracks lower influence between them (e.g. crosstalk)
Why? This reference point is very often used in Pick & Place output files. When doing assembling, machine will pick up the component at this 0,0 position.
Why? You need to know how to do it
Why? So the ESD pulse doesn’t travel through your board and it discharges immediately behind the connector
Why? It’s very useful for desoldering components like resistors, capacitors and even some chips
Why? Some components may get really hot and you may need to place there heatsink or find another way how to take the heat away.
Why? Because it’s one of the silly mistakes which you can make while creating a new component. It is often very hard to find and fix.
Why? You need space for mating connector and you may use boxed and unboxed version of header
Why? Many times, there may be something wrong from assembling process or you may damage some boards during testing.
Why? It will slow down the signal edge.
Why? It helps you to remember the changes in the next revision