Because a representation maybe convenient in a particular context. For instance, hexadecimal one uses exactly two digits to represent all of the values of byte (to display byte values with decimal representation you may need three digits, but a large part of decimal three-digits-numbers cannot fit in a byte); binary representation maybe opportune whenever you need to display a bit mask, and so on.. :)
If the Lord God Almighty had consulted me before embarking upon the Creation, I would have recommended something simpler. -- Alfonso the Wise, 13th Century King of Castile.
This is going on my arrogant assumptions. You may have a superb reason why I'm completely wrong. -- Iain Clarke