Head Height:  Most printers allow you to raise or lower the heads (ie the carriage that the heads are carried in).  Normally, the head height is modified to accomodate thicker media and/or media that has a tendency to perhaps buckle or cockle.  Typically, this is a due to a combination of a higher bed temperature, unstable media, or improperly adjusted RELATIVE temperature settings between pre-heat and printer bed-heat settings.  These temperature effects can affect print quality on their own, but that's the subject of another weekly tip.  If you suspect media cockling issues, then by all means raise the heads to avoid head rub or head crash.  However,  let's assume for now that the media is laying flat on the printer bed, under the heads.  If the relative distance between the top of the media and the bottom of the heads CHANGES, then placement of the dots will also change.  In this case, it is important to recalibrate (bidirectional calibration, typically) the heads, and also do a feed calibration to avoid overlapping or underlapping passes.  Many operators prefer to avoid the spectre of head damage by always printing in high head height.  However, there is a certain statistical "spread" governing the laydown of the dots (similar to the spread pattern of a rifle or shotgun), and the greater the gap, the greater the spread, and the fuzzier the image.  You will lose detail in this case.  In addition, the effects of air currents, and static charges (causing the bending of ink dot trajectories) will be amplified, also causing loss of image detail.  As heads age, and dot placement becomes less precise due to nozzle and head wear, the difference in higher head heights will become more pronounced.  Lowering the heads can thus have a dramatic effect on print quality, as long as media stays flat on the printer bed.  Understand what affects the quality of your prints, and control your equipement variables....and you'll be able to control print quality of your product!