The "nozzles" in an inkjet printhead are actually very tiny tubes, about the size of a human hair. One Epson printer has a resolution over 5000 dots per inch, which means the tubes are extremely fine. Each nozzle holds ink until given the command to eject it.
In HP and most other inkjets there is a tiny heater for each tiny tube, and when the heat is turned on, ink is ejected. Epson printers use "piezo" which is a heatless pump to eject the ink. But in order to be ready, there must be ink in the nozzles. And if the ink isn't used, it will dry up in time, making a clog. How fast it dries up depends on several things - environmental conditions like temperature and humidity, the size of the tube it's sitting in, and the type of ink being used.
Some ink manufacturers advise running some ink through the nozzles every day, which may be a little extreme for some environments and types of inks although probably just right for others. The action of running a small amount of ink through the nozzles on a regular basis will keep the ink from drying and will prevent or reduce the instance of heads clogging.
Harvey Head Cleaner is a program which will ask the printer to print a pattern similar to a nozzle check. You can schedule Harvey Head Cleaner to run only Sunday mornings, or only twice a week. or every day, or twice every day. The pattern we use for Epson printers uses a minimal amount of ink, but it moves ink through every nozzle.Harvey will awaken a sleeping or hibernating computer and cause it to print a pattern at your assigned schedule.
This will usually keep a printer ready to print, without having to perform wasteful head cleanings, and in most cases it will prevent or greatly reduce the number of head clogs. If you print a pattern like a nozzle check every day your print heads should remain clean and clog-free. That's what Harvey Head Cleaner does.
In order to work properly, the printer must be left on, the computer must be left on (although the monitor can be turned off) and there should be ample plain paper left in the printer. (Please remove the expensive art paper or transfer paper.) Harvey cannot work without paper, so load up with cheap paper. Then you can take that long weekend without worrying about your printer.