Any time you are thinking about making a decision that may have any significant impact on yourself or others, it is always a good idea to "sleep on it" or wait on your decision until the next day. This is a good idea in most cases because it gives you a little time to process it and makes sure you do not make an impulsive decision.
Often when you are in the moment, you may feel very strongly about something and you feel very passionate about it and want to go through with it right away. While this is ok and you may be able to get some good ideas together, you may end up making a rash decision that you will regret later.
A good example is if you are going to send an important email to someone. It might be for work or personal and you might have a strong opinion on something that you want to express to another person. Often a message like this can cause issues between people especially if they have a different opinion.
If you hold off on sending it and wait until the next day, often you will find the next day you feel differently and might not even want to send the message anymore. The next day, you will be in a fresh state of mind and will not be caught up in the heat of things so you are able to take more of an outsiders perspective and make a better decision.
Of course there are times when even after you sleep on something, you still feel the same way the next day. In this case, it reinforces your decision or thoughts so you know you are on the right track and not just making an impulsive decision.
Next time you are thinking about doing something spur of the moment that may have a big effect on yourself or someone else, be sure to give it a little time to make sure it is the right decision.