If you respond, it sets a precedent that you can be bothered at all hours – even on vacation. If you are the person sending the after work emails, you could be rubbing your employees and co-workers employees the wrong way.
The time stamp on a late night email might have your boss scratching his head. Sure, maybe you’re a night owl, but sending a work response when the rest of the world is sleeping might look weird.
You’re more prone to making mistakes. Don’t respond when you are tired because you are more likely to make mistakes and typos. Save your response for the beginning of the workday.
You need to switch out of work mode and relax so you can be productive the next day. (Pop Sugar)