This occurs in the liver. Natural substrates are bilirubin and thyroxine. Aliphatic alcohols and phenols are commonly conjugated with glucuronide. Thus hydroxylated metabolites can also be conjugated. Generally the resultant metabolite is more water soluble, and certainly less lipid soluble.
Less drug is reabsorbed from the kidney.
Occasionally the metabolite is less water soluble. A significant example is the acetyl metabolite of some of the sulfonamides. Some of the earlier sulfonamides are acetylated to relatively insoluble metabolites which precipitated in urine, crystalluria. The earlier answer this was the triple sulfa combination, now the more commonly used sulfonamides have different elimination and solubility properties and exhibit less problems. In most cases the metabolites are inactive, however, occasionally the metabolite is also active, even to the extent that the metabolite may be the preferred compound to be administered.