How useful are commentaries in a code?

Answer 1

You should always make sure you're commenting throughout your code, as it may help you track down mistakes in your code.
Additionally, if you work on a team in which other people may look at your source code, leaving comments in your code is a good way to ensure that your team members understand your logic.

Answer 2

Comments are really very useful for ourselves and to others to understand the code, what we have written actually... Those are helpful at the time we have forgotten what we wrote....

Answer 3

Prio1: comments that are up to date
Prio2:no comments at all
Prio3 and evil:comments that are garbage