Printing wet on wet simply means you can print each successive color without usually having to flash (or dry) any of other colors in between.
We use the word “usually” guardedly as there will be some jobs (especially on dark shirts) when wet on wet printing will cause smearing and affect the print quality.
During long print runs you may find that you have to wipe down the bottom of the screens periodically because of ink buildup. Many times this problem is unavoidable even when using high mesh counts.
Many ink manufactures have ink formulations especially made just for wet on wet printing. It is recommended that you experiment and see for yourself if these specially formulated inks help you with the print applications in your shop.