1.2. Why proper footprint is important

For low quantity and/or home built boards footprint details are not that important. When populating the board manually, soldering with an iron, a lot of small mismatches between the footprint and the actual part can be easily worked around.

The more the process is leaning toward serial or mass production, the more such little details start to matter. When using a pick & place machine and reflow soldering, a suboptimal footprint may cause occasional problems, such as misaligned parts or tombstoning. The worse the footprint is, the higher the rate of faulty boards coming off of the production line would be. Thus in most productions beyond the "few pieces of prototypes manually soldered" footprint quality matters a lot and low quality footprints can have a high cost (because of scrap boards or rework required).