Some scripts like WordPress and Joomla can leave a big error_log files that no one will ever look at. Try opening a 30mb log file with Word and see what happens. In most cases you can just remove this file with a simple command.
To remove all error_log files for CPanel accounts that are live use:
find /home/ -type f -name error_log -delete
To remove all error_log files from backups use:
find /backup/ -type f -name error_log -delete
This will take a while to complete because it will look through every file, it also runs pretty smooth so just sit back and let it work it’s magic.