Describing small things means using very small numbers. A nanometre is 0.000000001m. That's hard to write and illustrates the usefulness of standard form. 1 nanometre is 10-9 m. The same applies to very large and negative numbers. Tasks such as "estimate how many one nanometre-across transistors would fit on a pinhead of diameter 1mm?" encourage manipulation of numbers in standard form, especially if done without a calculator.