Hello lZ, this often appears in the proof questions. You have proved one thing, and if you want to prove the same thing again, you can use the same reason.

For example, if you prove that △ ABC △ A 'b 'c' (SSS) is too annoying to use SSS in the same problem, and prove △ def △ D 'e 'f', you can use the same reason at this time.