What Test Automation won't do for you ?
Test Automation is a main stream activity and it's goal is to strengthen the rapid pace of development and augment the continuous release process. In order to keep up the with the pace of development, there has to be a sustained effort to maintain and update the test automation suite.
So test automation has to be a planned activity and included/incorporated in the project planning.
This post is to highlight what test automation won't do for you. This is mostly out of my experience and conversation with different people from various roles. Definitely when you read you will have more to add or subtract (which is fine and individual's opinion).
Test automation won't substitute for manual testing. It's an on going activity. It's not a one time investment. It's a sustained effort and hence needs to be treated as test development. Coming onto Test Automation pass percentage, I know this number is the most talked about among QA's of different team. But even having a pass percentage of 100 doesn't guarantee that your product is bug free. It just assures you that your automated test cases are working as per the expected result. Also a different perspective would be what ever was working before is still working fine. It however implies that the probability of finding bugs is lesser. But it doesn't cover up for the manual testing activity which was not automated.
Your test automation suite is not intended to find new defects! All you are trying to build by automation is a safety net where in you can get an assurance that whatever was working before will work after as well. Did you notice that you are not putting any kind of intelligence in the test automation. So it will only test the system against the business scenarios and the defects you found and have automated. Test Automation suite is not intelligent. It just saves you from the monotonous routine of running the same step again and again and in an efficient way.
So in short test automation is not the answer to lot of your questions. It's just as smart as we can create it, which is obviously a time taking and gradual process.