It depends both on everything your outputting and what your workflow. Here some general tips . Everything in XD is in Vectors so you should be able to design at 1x and then scale up or down to whatever you want. You can also export as SVG and that will scale as you do. If you need to have a variation at a specific resolution (like icons) you can create an artboard at that pixel size and export the whole artboard.
Hope that helps in your workflow. Thanks for using Adobe XD!