In what field are ens and ems used in?

Back in the olden days of printing when newspapers and job printing was done with handset type (assembling one letter at a time) and by means of a linotype, ens and ems were blank spaces. An en was the width of a number and a thin space was the width of a comma or a period and were used in doing tabulation. An em was the width of the size of type that you happened to be setting type in. For instance, if you were setting type in 12 point type, an em was 12 points in width and twice the width of an en. The same rule applies to en dashes and em dashes.