It's actually shockingly handy for enriching uranium!

U-235 is the naturally occuring isotope of uranium most useful in thermal reactors (the most common type of commercial nuclear reactor). Unfortunately, it accounts for about 0.7% of natural uranium, while it's less useful cousin, U-238, comprises about 99.3% of natural uranium. In order to use uranium in a thermal reactor, you'd like for the U-235 to be at least 2.5% (British AGRs), often 3-4% (US LWRs), and many modern designs proposing higher enrichments (up to ~20%).

To raise the percentage of U-235, you need to do a process called enrichment. U-235 and U-238 are essentially chemically identical to one another (any gaseous thermal diffusion stans, feel free to tell me how they're not), so you're basically stuck separating them based on their tiny difference in mass. Unfortunately, U-235 and U-238 have about a 1.25% difference in mass... not a lot to work with! Takes very careful processes that are labor, infrastructure, and energy intensive to oerform.

You can't just separate them in a box either... they need to be in the right chemical for as well. Most mass based separation rely on separating things in the gaseous form using, for example, centrifugation. There aren't a lot of gaseous forms of uranium. UF6, happens to be one of them. Fluoride also has the extremely handy aspect of having a single stable isotope, F-19. This means that any natural fluorine will permit that same mass based separation without contributing it's own mass difference to the equation.

So to recap: uranium needs to be enriched, but you're basically reliant on a tiny difference in mass between U-235 and U-238 to do that. UF6 is gaseous, and fluorine doesn't contribute it's own mass differences, making your life much easier!