Whether you're writing an essay or a lengthy response to a troll on reddit, it's important to take regular breaks from typing to help your hands, and keep your mind refreshed and focused. It's a habit easier said that done, so making use of a timer app to remind yourself to take a break can work wonders.
Kettle's on! Pizza's in the oven! Only 23 minutes until a new episode of Inspector Spacetime - all are situations where keeping an eye on the time is important. Now hopefully you're not like me (i.e. useless at doing so) but, should you be, then TeaTime is a neat Unity-launcher based alarm applet that works wonders.