What's the point of using a tool like Figma?
Why not just build the site in Webflow directly?
For many site builds, this is accurate- especially if you're using a template as the basis for your site build.
However if you do custom website designs starting with a blank page, Figma is like digital whiteboarding on steroids.
Approach
You can quickly work through the WHAT you want to build before solving for HOW. In advanced designs that's important, you don't want dev hours prototyping a quiz feature you may never use.
Versatility
Also, since it's platform agnostic, that same design could potentially be used to build on another platform like Shopify if that were necessary, and more designers know Figma than know Webflow, so it's translatable.
Easier Site-Wide View
The canvas is also preferred by some, because you can zoom out to see multiple full page layouts and multiple pages side-by-side. That's just convenient and helps you maintain cross-site design consistency more strongly.