Comment by WHoWHo

From my experience in 20 years of Java, it prevents the reusage of local vars, which mostly is wrong.

   Person p = ....
   p = doSomething(p)
   ...
   p = doSomethingElse(p)

is hard to reason about when it should be

   Person p = ....
   ... lots of code
   Person updated = doSomething(p) 
   ... lots of code
   doSomethingElse(updated)

Which is easier to read and understand. So you might have had bugs that would have been prevented with final, but you didn't attribute to final.