It is most important! A high quality coffee machine will produce great coffee but if the coffee has been ground by a sub-optimum coffee grinder then the quality is significantly affected. A cheap grinder can burn the oils in coffee before you’ve even brewed it. Blade grinders are the worst offenders unfortunately! They produce a grossly inconsistent grind and simply destroy any flavour and should be avoided. Burr grinders are highly recommended! A pair of burrs consist of a bottom and top plate which have sharp groves. These spin in opposition to each other and depending on how far apart they are from each other will depend on the texture/size of the grind. The bigger the burrs, the more efficient they are and heat dispersion is improved. This is more important when larger volumes of coffee need to be ground. 'Step-adjustment' coffee grinders are far less accurate than 'Stepless' coffee grinders. For pairing with high quality coffee machines and brewing espresso, the latter is required as it gives more control over the size of the grind and therefore the timing of the extraction.