I pointed to one bug: error messages are not redirected to stderr in shell scripts. It's small bug, because it will affect development only, but I found it. I need to find just one bug to prove my point, isn't?
If you redirect stdin to /dev/null, to see error messages, you will not see these error messages. If you try to grep them by "error" keyword, you will not see them either. So you will have two options — read everything using your own eyes OR fix bug in the script. So this is the bug, which causes significant time losses for OPS team pretty often (once 2-3 months someone is bitten by that).