Best practice old vs set_value

Hello,

does it make any difference on using old instead of set_value?

thanks

If you are using the form helper, this feature is built-in. You only need to use this function when not using the form helper.
https://codeigniter4.github.io/CodeIgnit...s.html#old

ci-phpunit-test | CodeIgniter Testing Guide | CodeIgniter 3 to 4 Upgrade Helper

I'm just using plain html, and the docs show old and set_value.
I don't know the difference between these too and was wondering what the best practice (most developers) use.