It matters sort of like lifetime MPG or L/100km would, but in very different ways to the point that it would be misleading to make any statement from the number.
A high Wh/mi Model 3 could indicate that the owner tends to not precondition the cabin. Since the meters (including the "Lifetime" meter) only count energy when not in Park, someone that only uses climate control while driving will show higher energy usage than someone who preconditions the car routinely (since the preconditioned car will use less energy for climate control during the drive). If they have a very short commute, not preconditioning will result in a crazily high number. But the fact is, preconditioning will almost always use more power than not preconditioning. This goes for things like Cabin Overheat Protection too, which is a sort of mild preconditioning for when it's hot.
Because climate control can be such a large part of the usage, it's highly inaccurate to interpret a high Wh/mi as the car being driven hard. You can accomplish a high Wh/mi simply by driving slow, short commutes with the heat on comfortably. This isn't because the climate control is a huge drain either - you can expect about 8kW max for climate control (usually dropping to 3kW or less quickly), whereas cruising on the highway takes about 12-18kW just to maintain speed. In this way, the highway is "harder" on the battery, but probably results in a lower Wh/mi figure.
A better measure would be battery cycle count, as it would account for standby usage, preconditioning, and driving. This info is known on the car internally, but there is no way to see it on the screen. Still, that gives no visibility into things like how often it's been floored, driven to 0%, stored at 100%, etc. You're never going to get that sort of info, much like you can't really get that info for nearly any ICE vehicle (and inferring it from things like MPG is full of confounding factors).
