Not being smart but I was told:
"People log Hobbs, Airplanes log Tach."
You may belong to a club or have a deal with an FBO for using a plane based on Tach (engine wear), but your logbook is meant to reflect the "clock" hours you spend in the plane.
If you want an example, the airlines track two times - "block" and "flight". Both are run off the time of day - there's no tachometer that I know of in a jet.
Block is the elapsed time from when the door closes and the beacon goes on (still at the gate) until the door opens and the beacon goes off (at the arrival gate). This is (usually) the time the pilot records in his/her logbook and is the basis for his/her paycheck.
Flight is the elapsed time from "wheels up" (departing or lifting off the runway) until "Weight on wheels" (touchdown). This is (usually) a maintenance number to determine how many "flight hours" the airplane has accrued. And just to be fair, there are some operators where this is the basis for the pilot's paycheck - unfortunate, but true. I have worked in a place where the pilot gets paid "Flight hours plus 10 minutes" - meaning they encouraged us to close the door and get to the runway in a hurry and do the same getting back down.