The pgBadger tool condenses and ranks error messages for easy viewing, and produces a nicely formatted report in HTML. From that report, you can find out the most frequent errors.
As a rule, it is good practice not to tolerate errors in database logs if you can avoid them. Once the errors start showing up in the log and report, you should find their cause and fix them.
While it is tempting to leave the errors there and consider them as just a small nuisance because they do no harm, simple errors are often an indication of other problems in the application. These problems, if not found and understood, may lead to all kinds of larger problems, such as security breaches or eventual data corruption at the logical level.