I use it for the same reason as Jerricho.
An example:
An aeroplane that has already been spinning in the hold for 15 minutes before being transferred to the director might get confused when he is told on first contact that the "Delay is 15-20 mins". Is this total delay or remaining delay / delay from now?
As a general rule, some (including me) use:
A/C not yet holding - "Delay 15-20 mins"
A/C already in hold - "Total delay 15-20" or "delay another 5 mins"
To most LL based crews, I'll use the first option, whether they're already in the hold or not.
Nothing in the book about this - just makes it less ambiguous.
AI