Epson states that if you have inserted a cartridge into your printer and have not used all the ink within six months you should discard the remainder of ink and buy a replacement. An alternative to this is removing the cart and gently shaking it every few weeks so that you can prolong the use of the ink.
If you do not do this, the pigment in the cart begins to settle. The outlet port is in the middle of the cart. The ink therefore can be denser or thinner and it does affect color.
If you do not use your printer very often, the Epson ink inside the ink lines of the printer also begins to settle and eventually it forms a lining of thin solid pigment. This can dislodge in sheets and fill the dampers. PiezoFlush is engineered to dissolve it and break it up into particles.
All Epson pigment printers are made for "professional" type users who are expected to use their printers frequently. Ink wastage in this case (trying to make up for not using it) is not ink wastage - but preventative maintenance to prevent expensive repairs. Use it or lose it applies very much to Epson pigment ink printers. They never tell you this...of course!