Using my fast coffee scale for cocktail creation is efficient and eliminates the need to wash my jigger. I round to 30ml for one jigger and 15 for a half. This is easy to remember as those are the volumes of a standard espresso shot and a ristretto respectively.
Cheers! 
I do this too. The principle also applies to baking, where you not only save washing measuring cups, but everything is more consistent.