WHICH PROBLEMS SUCH RESIDUALS CAN CAUSE IN AN INSTALLATION?

It surely depends on the kind of liquid and on the application.
Let us take water as example.
In irrigation installations water is often taken from sinks, canals or lakes and is not treated. The systems clogging may be caused by a chemical and biological combination of the present elements. Think about those jelly whitish compositions due to sulphide acid oxidation (characterised by the classic rotten eggs smell). Or the reddish mud due to bacteria work. Or even worse that weed, typical of stagnant shallow waters basins, also known as “water lentils” and widespread all over the world.