Your children

Can, and will, download stuff overnight, pr0n, music, movies, etc.. violating copy right laws, etc.. The following image is a snapshot of a customers 7 day modem activity log, showing that on average, every night from 11PM till 3:30AM, there is an incredible amount of downstream activity, and from 11PM till 7:30AM, there is an even higher amount of upstream activity out of their computer, causing slow speeds.