The downside of using Modafinil to stay awake for longer periods maybe there. Some people use it temporarily for jet lag or once in a while after a late night but regular use may disturb sleep wave architecture long term or potentially lead to dependence. Slow wave sleep is the sleep in the initial period which is disturbed by Modafinil. Long term effects will probably emerge after a few years so use should be avoided or limited to only occasionally and not every week. Eg cognitively, initially nicotine enhances cognitive function. But later one uses nicotine to bring back cognitive function to normal baseline. So Modafinil may do the same. Normal brain with no drugs is the best rather than using drugs to increase cramming that we are not certain of yet.