It does take a lot of extra work (using walls-o-water and bubble-wrapped cages, restaking during windstorms, reinforcing the protection for unseasonably cold nights, etc.) and in my climate I can push the tomato harvest maybe a week earlier for every 2-3 weeks earlier that I plant them, so it's not a huge gain.
With some extra work, you can extend your season in both directions by using row covers, cloches, and other ways to protect your plants. It does take a lot of extra work (using walls-o-water and bubble-wrapped cages, restaking during windstorms, reinforcing the protection for unseasonably cold nights, etc.) and in my climate I can push the tomato harvest maybe a week earlier for every 2-3 weeks earlier that I plant them, so it's not a huge gain. If I had a greenhouse, I could try to extend the season even more.