You can use it when your hands are sticky - like when you're in the kitchen and you need some recipes. This is not a really good sign, because when Apple was trying to sell Apple II+ computers in 1979, they tried to get people to think that they would use them to store recipes. But anyway. Take a look at this demo video, which actually does have some interesting ideas.
A loud clatter of gunk music flooded through the Heart of Gold cabin as Zaphod searched the sub-etha radio wave bands for news of himself. The machine was rather difficult to operate. For years radios had been operated by means of pressing buttons and turning dials; then as the technology became more sophisticated the controls were made touch-sensitive--you merely had to brush the panels with your fingers; now all you had to do was wave your hand in the general direction of the components and hope. It saved a lot of muscular expenditure, of course, but meant that you had to sit infuriatingly still if you wanted to keep listening to the same program.
Zaphod waved a hand and the channel switched again.