The metric system is used because it is based on the number 10. Ten is easy to use for mathematical operations and conversions.
It is also easy to use for scientific notation when you are referring to powers of ten. There are extremely large and extremely small numbers in science. Thus, scientific notation allows for accurate abbreviated ways to symbolize these numbers. For instance, if I were to say 1,000, in scientific notation it would be 1 x 10 ^3. If I was to say 1,000,000, I would scientifically write 1 x 10 ^6.