Update: I've just read the answers to this question Why do users feel the need to notify each other [+1] when they upvote a question or answer? , apparently they provide good answers to this question as well which means I am voting to close this question as a duplicate of that one.
I was unable to find it by searching for it and only found it as a related question to another question when looking. This means that closing this question as a duplicate would likely assist users who will look up this subject in the future.
I've read the FAQ and to the best of my understanding this is where I should ask this.
A lot of times in Stack Overflow and other Stack Exchange websites I notice comments in the format of:
+1 good answer, also I'd like to add...
+1 I'm upvoting this because...
-1 you should have said...
I was wondering if writing this sort of comments is considered bad manners since it kinds of beats the purpose of anonymously voting on questions. For downvotes it makes sense since you're giving criticism, but still you don't have to include the -1 in the comment.
Here is some related reading raising some points for and against it in the following post about a suggestion to make these mandatory +1 / -1 in comment
I have also found this strongly related but somewhat different question Why do users feel the need to notify each other [+1] when they upvote a question or answer?