I got Win 10 IoT core on my RPi 3. I dont have a computer running Windows, therefore I cant really run the dashboard. Is the Windows 10 IoT OS still useful? Or should I just switch to Raspbian.
You better switch to Raspbian as without Windows PC it is completely useless. You need Microsoft Visual Studio installed on a Windows 10 PC to install and run packages. As far as the usefulness is concerned you will not find any prebuild packages to run, you have to create your own software using Visual Studio IDE which is based on Universal windows platform.