It depends what you use your computer for. If you spend most of your time online, Ubuntu can be a great tool to have around because, as I said earlier, it’s inherently more secure than Windows. Not only does it have a built in firewall that configures automatically when you install new software, but there’s just not that many viruses designed for it.
Also, there’s a lot of advanced scientific tools that only run on Unix-like systems. If you need that it’s good to have around.
But if you’re perfectly happy with your Windows set up, there’s no real need to dual-boot. It’s all about your preference. Though, having a Ubuntu partition might be a great failsafe backup if your Windows partition ever breaks…you can get at all your files in the other operating system.