This has quite a few consequences:
* it creates unnecessary extra iterations in the reviews
* which in turn creates extra workload for reviewers
* it also creates extra workload for contributors
* ultimately, it impacts the working relationship between reviewers and contributors
In addition, it affects review statistics. For example, a patch series of 15 patches where 1 comment is not addressed in consecutive 10 series, can lead to an extra 150 mails related to that series. Assume this happens in 10 larger series, we are talking 1500 mails related to code reviews (not counting any replies). To put this in context, in 2014, 5622 patches were sent for review.
= Possible Solution / Improvement =
Precise how-to's for contributors.
Code checking tools may also help, by reducing the number of comments, reducing the number of comments that need to be addressed
The challenge is that this is a manual process, which can easily be gotten wrong. There are probably also several ways on how this can be done effectively and what works for one person, may not work for another.
When using review tools such as Gerrit, it is really easy to see whether all comments have been addressed.