Disadvantages of automated functional testing

Disadvantages of Automated Functional Testing

1. The machine used for running scripts gets occupied until the test automation activity is finished(true for Selenium, Appium, WinAppDriver, and CodedUI). 
2. Small mistakes at the wrong time can fail your automated testing scripts. For example, hitting the enter key while UI automated testing is in progress might cause an unwanted popup or a form to submit, which could lead to a test failure.
3. Automated black box testing (a.k.a functional UI testing) is slow. (true for Selenium, Appium, WinAppDriver, and CodedUI)
4. Many resources are needed to run multiple tests in parallel(although it might not be possible to run specific tests in parallel due to application domain requirements).
5. You can't pinpoint the cause of the fault, you only get to know the steps to reproduce, and the developers have to find the root cause of the bug later.
6. Automated functional tests are flaky and fail due to small changes in the application UI. 

Automation testing is the buzzword of the day. But we must know that some types of test automation are less valuable than some other types of automated testing. 

Not all automated tests are created equal.

UI-driven testing, known as end-to-end or functional testing, is, on the surface, the easiest to get going. As a result, tools like Selenium, Appium, Coded UI, WinAppDriver, WebDriver.IO, and PostMan are in high demand. But there are still some disadvantages of automated UI testing, briefly summarized here for you. 

The best thing you can do is to automate unit testing and then integration testing. That's where you're going to get the most coverage.