Nothing converts energy to 100% heat, but I do understand what you're trying to say. Your definition of the word "efficiency" is different than that of most people's.
For example, take a lightbulb with a dimmer switch. Let's also consider the bulb will create 60% heat and 40% light. All of the energy that is put into the circuit will come out of it - it's 100% efficient in that frame of reference, but that's a law of physics: energy cannot be created nor destroyed. In that case, you are correct - all of the energy is used. However, when people generally use the term efficiency, they mean the ratio between what you put in and how much you get out of what you want to get out. The point of a lightbulb is to make light, not heat. In that case, our example light bulb is indeed 40% efficient, because we put in 100% electrical energy, and we only got 40% back of what we wanted, light. Since the lightbulb is connected to the dimmer, the dimmer also has an efficiency, converting some of our 100% electricity to heat and electricity (but a lesser amount). Thus, our bulb outputs less of what we wanted since it gets less power (which is scientifically less efficient, but the trade off in real life is that you can vary the light level!).
In other words, since the heat is not what's desired from the bulb, it is considered inefficient. While heating the home may be a good thing in some cases, it's not in all (heat is a very bad thing to have in your home in the desert, or in Florida). However, anyone who buys a light bulb wants light from it: thus, the light is desired.
Edit: Consider a car. If I put gasoline in the engine and start it, wait until all the gas is gone, and get out, not having gone anywhere, is that 100% efficient?