For transmission, a leading space takes up exactly the same amount of space. For use on the receiver, the leading space is much easier to deal with than a leading 0, because a leading 0 is how functions that convert strings to numeric values know that you want the number interpreted as an octal value.
It is unlikely that you will be sending values less than 100 as octal, while sending values greater than or equal 100 as decimal.
Unless you are really weird, that is.