The standard system of measurement is what is popularly referred to as SI unit (or international system of units). For example, the SI unit for length is basically in meters (m), which is convertible to millimeter (mm), centimeter (cm) or even kilometer (km).
If there is no standard system of measurement,
1) Scientists will not be able to compare data as every scientist will use a unit that suits him/herself which might make data incomparable as some units might be difficult to convert to other units or there conversion methods might even be debatable.
2) There might be a general lack of understanding of the research work done by a scientist/scientists in the scientific community. This is because the standard system of measurement affords scientists to communicate properly with the same or convertible units and based on 1. above, if scientists use any unit that isn't agreed upon, different/unknown/debatable units might make understanding of research works incomprehensible.
