In software testing, there are many processes that do NOT fit the need of complete automation. Partial automation allows the organizations to observe the benefits of automation without the involvement of too much cost and time.
There are few test cases that cannot be automated for many reasons. In such cases, the automation is done to the level that is very much beneficial and the rest of the tests are executed manually.
Below are the potential candidates for partial automation:
Tool limitation - Tool Doesn't provide the methods to access those objects.
Poor ROI - Investing time on few scenarios that might NOT be cost effective even over a period of time.
Time for Execution - Some scenarios in automation might take more time to execute than manual tests.