As with the days and seasons, it would be odd not to include a day and night cycle. Whilst you should be resting and sleeping your character at night, there might be some benefits to going out in the dark once in a while.
Special flora might only come out at night in particular season that is a vital ingredient in certain potions to make. The same could be said for particular fish. You might also stumble across special interest areas that appears under the night sky. What looks like an empty ruin during the day, could be teeming with demonic or undead creatures during the night.
Be careful however. There are far greater horrors that lurk in certain areas at night than during the day. What could be a harmless stroll at dusk outside could end up resulting in a nasty encounter which will hinder your daytime playing experiences or simply leave you dead on the floor.
I’ve just started the doing the cycle and shouldn’t take too long to do. The interesting part will be the hidden explorable areas for you to find and events that take place.