Which test case should not be automated?

These types of

test cases should not be automated

1. One Time testing. (Non Repeatable)
2. Ad-hoc Testing (As soon As possible results required)
3. Usability Testing.

Which test case should be automated?

Following

test case should be automated

• Test case need to be run for every build of the application
  (Sanity Testing)
  
• Test that use multiple data values for the same actions.
  (Data Driven Testing)
  
• Critical Application functionality.
• Business functionality which won’t be change in short time period.
• Performance testing
  (Load & Stress)
  

What are disadvantages of automated testing tools?

Automated tools have following disadvantages.

Usability Testing:
Usability of software can not be automated so automated tools cannot rate the usability of an application.

Cost:

 Usually these are licensed so automated tools are quite expensive

Programming knowledge required:
 To customize test scripts according to test requirement.
Test maintenance is costly: In case of playback methods.
Even though a minor change occurs in the GUI, the test script has to be rerecorded or replaced by a new test script.