Engagement: only tool and computer system work so there is no chance of being bore with the manual style of testing. On other hand manual testing often gets bore when we repeat same thing again and again. For complex software, same script runs for many days without any human intervention, can we imagine same thing with the manual testing that someone will work for many days.
Approach for testing: when same test case needs to be repeated many times then automation is the best solution. On other hand, manual testing has entirely different approach where there is imitation when it comes to repetition.
Approach for the build verification testing: this is mainly possible with the automation style of testing while manual testing is not that feasible when we consider build verification testing.
Deadlines: in the software industry, this term is extremely popular that there should be any deadline for the product. When there is complexity in the project then deadline is often missed. When you run testing through automation tool then there is no chance of failing deadline while condition is quite different when we consider manual testing. Sometimes manual testing takes far more time than expected.
