Alphanumeric fields are left-aligned below one another. Numeric fields, in particular if they are to be compared with each other, are right-aligned below one another.

A user finds alphanumeric values by searching through the first letters of a list on the left-hand side; it is for this reason that the left-alginment is to be preferred.
It is easier to compare numeric values and to locate them in a list, if the amount of the value is also indexed by means of the right alignment.