Hashes which appear in the format definition are replaced by numerals (ie any of nought to nine) in your worksheet. Zeroes will always appear, unless replaced by actual parts of the number. For example, in a number style 0,000, 10 will appear as 0,010, whereas if the style is defined as #,##0 it will appear as 10.
Where characters after the decimal point are represented by hash signs, trailing zeroes will not be displayed. For example, the format 0.## will cause 54.00 to be displayed as 54. If figures after the decimal point are displayed as zeroes, trailing zeroes will be displayed. So for currency formats, where you want decimal places always to be displayed, you need to ensure that the format ends with .00.
Enter the unit number format character as a zero character, especially if it is followed by a decimal point and places. This will ensure that numbers between 0 and 1 have 0. in front of them.