Checkpoint Files - Performance Issues w/ Loop Containers

During an interview today I asked a candidate if she had experience using SSIS Checkpoint functionality. Although I haven't confirmed what she told me, I suspect that it is true. She said that she has experienced performance issues related to using Checkpoint files in packages containing loop containers. My guess is that SSIS tracks the value of the variable being used for the loop counter in the checkpoint file. Writing a value to disk for every iteration in a loop probably has very significant performance effects.