Long ago, when the earth was young, Dwight christened this the Oingy-Boingy tool and that is what I have called it ever since.
It's very easy to use, start to drag, active the tool, and then click on the start point and then the end point and it will place what you are moving at the midpoint if that is what snap point is set to. Or if snaps is set to divisions such as 5 you have the choice owhich 1/5 point between you want to move the element to.
Distance snap option works similarly
Percentage works slightly different in that it requires you to have the element you are moving at the start point to move it that percentage distance and you will not an option of every 20% e.g.; just the one 20% of distance.
Erika
Architect, Consultant
MacBook Pro Retina, 15-inch Yosemite 2.8 GHz Intel Core i7 16 GB 1600 MHz DDR3
Mac OSX 10.11.1
AC5-18
Onuma System
"Implementing Successful Building Information Modeling"