Psychological reasons only
Can't think of a logical reason why I did this.  It's exactly like saving money for something you may want to buy in the future, but in the meantime you're tying up cash for this privilege.  I do it because it feels good to have a balance there, almost like I can buy something new without having to pay for it!  So for me it's purely psychological.  If anyone can think of a more logical reason, please let me know.
Rating: 3 stars