Preloading key request can be very important to speed up rendering the page, and avoid Flash of Unstyled Text (FOUT) issues.
If Critical CSS is enabled, Swift Performance can preload all fonts automatically which can be found in Critical CSS. If you found some of them is unecessary, then you can exclude it by URL (or URL part).
You can also use Manual Preload Fonts feature, which will work even if you are not using Critical CSS. You should use full absolute URLs here.