Water bath gets up to 212°F (boiling temp) which is ok for canning high acidic food like fruit and tomatoes. When you add pressure by using a pressure canner you can get much higher temperatures that are required for canning low acid food like meat and veggies. If you get a stove top pressure canner you can use the pot for water bath canning too so no need to buy two things.
If you are just getting started with canning here is more info heart https://minisliceoffarm.com/2021/08/getting-started-with-home-food-preservation/