| Heft is also the feeling the weight, density, and balance of an item gives you when you first pick it up, a kind of "mouth feel" for the hand.
Our predilection for items, tools, and devices with heft stems from the physical nature of life. Hammers smash and batter, knives cut and carve, and clamps and levers squeeze, lift, and crush. Our tools have to be rugged because they are called on to do rugged things. A thing with "heft" has good balance, solid construction, and a material density that creates a feeling of "rightness" in the hand. This impression is most markedly apparent the first time an object is picked up, especially if the feel of the item doesn't match our sight-based expectations. The fake Rolex looks fantastic until you pick it up.
A quality device fits well in the hand and is easy to handle. How an item balances in the hand is as important as how well it is made. Look at a pen, or a modern cordless power drill, or a nice piece of luggage. A good tool almost begs you to use it, giving you a feel of power and capability. It leaps to the task, be it dialing a phone call, making a hole, or writing your name. A well-built but poorly balanced item may carry a certain heft, but will be found lacking, even if the wielder cannot explain why specifically.
Ergonomic layout is also a factor. If a thing feels great in the hand and balances well, it doesn't work it the controls are in an awkward place. This isn't only the concern of electronic devices. A pocket knife that feels great when open or closed, yet is difficult to transition between the two states, is a poorly designed tool. Balance and ergonomic design is the "feng shui" of a device.
Some would argue that the advent of electronic products has minimized the value of heft, as they argue that a device's power and capability is no longer directly linked to its construction. Their position is that the attributes that contribute to heft are important for mechanical devices, but are not concerns to an electronic device. A typwriter has to be sturdy because to operate it, you bash levers that swing a little hammer to strike an inked impression on paper. An electric typwriter merely replaces the first step with an electric switch that drives a motor which swings the hammer to strike the paper, so it too needs to be solid. However, some argue that an electronic word processor with voice recognition software and an inkjet printer can be made without a concern for heft. I disagree.
I feel that heft in electronic components will always be important, albeit as more of a cosmetic concern than an operational one. Touch is still our primary interface with the physical world, and how an item feels is important. One doesn't need to make something heavy to have heft, it only needs to be well-constructed with an economy of space (high component density) and of quality materials. The aforementioned word processor's quality and performance will still be enhanced if constructed with a mind to fit, finish, and material quality. That inkjet printer doesn't have to massive and heavy, but in order to operate well (to keep the lines straight on the page, for example) it still needs to be made well and strongly to tight tolerances.
Heft is important as dealing with the physical world will always require good tools. | 
