Why do scientists control the number of significant digits in calculations involving measurements?

To maintain the precission of the measurement while avoiding reporting irrelevant digits.

Explanation:

Significant digits are the number of digits used that would contribute with the accuracy of the measurement, depending on the size of the number is started to be counted after the first non-zero digit.

Scientists control the number of significant digits in calculations involving measurements the more digits, the more precise the calculation is. Scientists often use scientific notation to work with very small or very large numbers in a more organized way, because it allows to write the numbers in a compact way.