I don't see why this could be bad. I think memorizing helps to keep you and your brain in a sharp condition. If someone want's to memorize alot of numbers, he or she will probably start to tell a story in their head. Then it begins to become more interesting because you have to be inventive an to be able to remeber your story in detail:
That's why some people who have synesthesia ( seeing for example numbers as colors) can memorize numbers better. I for example still remember a certain number, namely the number of a bolt in the serie 'prison break'. It was 11121147 ( very stupid, I know
). I see the number as a variation of colors and that variation sits in my mind. Another example is seeing the days of the week as colors.