Knowing how to tamp coffee properly is important because producing good espresso coffee is all about achieving the perfect extraction and producing good espresso coffee all the time is about achieving perfect extraction consistently. Tamping coffee properly is all about consistency and evenness of extraction. By tamping, you are trying to create an even ‘bed’ of coffee that, when inserted into your commercial coffee machine, will allow water to pass through it evenly.
For water to pass through evenly, at pressures of up to 9bar, the coffee bed must be perfectly flat, and without any cracks or discrepancies of density. Water at this kind of pressure will exploit any fault in a coffee bed and will pass through the path of least resistance. This will cause areas of your coffee to be over-extracted and other parts to be under-extracted leading to a poor-quality coffee.