Quick take
v0 is Vercel's AI builder that turns prompts into UI and full-stack web apps, with a visual Design Mode, GitHub sync, and one-click deploys to Vercel. It fits designers, founders, and frontend developers who work in React and Next.js and want a fast path from idea to live app. Its real limit is that it is built around Vercel and the React ecosystem, so it is a weaker fit if your stack is elsewhere.
Best fit
Use v0 when you want a clean UI or a working web app quickly and you are comfortable in React, Next.js, and Vercel. It works well for landing pages, dashboards, marketing sites, and app front ends where you plan to review the code and keep iterating.