It simplifies adding, subtracting, and comparing fractions.
As long as the ratio between numerator and denominator is the same, the fractions represent the same number.
For example: because they are all multiplied by 1 written as a fraction: It is usually easiest to add, subtract, or compare fractions when each is expressed with the same denominator, called a "common denominator".
For example, the numerators of fractions with common denominators can simply be added, such that
[2] The LCD has many practical uses, such as determining the number of objects of two different lengths necessary to align them in a row which starts and ends at the same place, such as in brickwork, tiling, and tessellation.
In musical rhythm, the LCD is used in cross-rhythms and polymeters to determine the fewest notes necessary to count time given two or more metric divisions.
For example, much African music is recorded in Western notation using 128 because each measure is divided by 4 and by 3, the LCD of which is 12.
The expression "lowest common denominator" is used to describe (usually in a disapproving manner) a rule, proposal, opinion, or media that is deliberately simplified so as to appeal to the largest possible number of people.