As implied by the name, scientific notation is most commonly used by scientists. According to the Franciscan University of Steubenville, scientists who must work with very large or very small numbers often use scientific notation to make such unwieldy numbers simpler to use.
Scientists that use scientific notation extensively usually work in fields that examine really large things and distances or really small things and distances. For example, according to the Institute for Energy and Environmental Research, astronomers often use scientific notation when making calculations. Astronomers must work with very large numbers, such as the speed of light, which can be written as 300,000,000 meters per second or, more simply as, 3.0 x 10^8 meters per second. Geologists and physicists must also use scientific notation to deal with very large numbers.
At the other end of the spectrum, microbiologists and doctors have to work with very small numbers. For example, the influenza virus is about .0001 millimeters in diameter. This is easier to write as 1.0 x 10^-4 millimeters. Engineers also need to use scientific notation from time to time.
Some careers use scientific notation to deal with both large and small numbers. For example, chemists must be able to discuss the size of molecules, which are very small, and the number of atoms in a substance, which is usually very large.