It would not be a good habit because anything of importance will be lost unless we transfer it to a piece of paper or commit it to our memory. I have seen people write on the palms or do some calculations, Unless we do it with a permanent marker like pen, it would be erased easily and no one would you a permanent marker on the hands unless they have no choice. I write down on the palms sometimes when i cannot find a paper when I get a number or a longer figure told over the phone by somebody. Now with the smartphone, most use it to type something as a memo and save it as a draft. In small hotels in rural areas that are run by a couple of people, I've seen them quickly jot down the price and tell you after you finished breakfast or lunch. So, unless it is an emergency and we have no options, it is better to jot down the important things on a piece of paper or save in the mobiles.