One of the biggest advantages of 4K resolution is having more screen real estate, which means you'll have a lot more space to work with. That makes it great for multitasking – the more space you have, the more tabs, windows and applications you can open and make immediately accessible.
4K monitors are not necessary for office work. However, you might find it extremely advantageous to use one, especially if you tend to juggle different tasks at the same time.