Commas are necessary for numbers in order to make things easier to read. Commas should be used every three numbers. For instance, instead of writing 2907, you should write 2,907. Commas in numbers are especially useful the larger the numbers get. For instance, note how a comma makes the following number as easily identifiable as in tens of millions without having to really count out each digit because the comma will separate things by 3s: 10583968 vs 10,583,968.
