That seems very odd to me. I would expect most people should have learned the impact of this from the first time learning addition. I guess this is a good example of why you can never assume to know how someone else thinks about information.

  |  5
  |+ 10
  |----
  |  15

  |   5
  |+ 10
  |----
  |  15

As beart says, it helps with arithmetic by lining up the 1s, 10s, 100s. Also, it makes it easier to compare which number is larger/smaller--very useful when dealing with currencies.