Figma is where I work through interface ideas, from rough flows to components and prototypes.
Why I use it
Most interface work starts messy. Figma keeps it cheap to move things around while the structure is still changing. I add precision once the idea has earned it.
I use it to compare directions and work out the interaction model before implementation. A prototype also gives everyone something concrete to react to, which is much more useful than debating an interface from a document.
I still make plenty of design decisions in code once real data and behavior are involved. Figma handles the early uncertainty.