The aim of this testing is to improve the end result desired by the marketing being deployed.
Significant improvements can be made to the results by changes in copy, layout, images, colors, video and split testing allows for the different elements to be tested for the same landing page.
Carefully measuring the result of the experiments is crucial with metrics. Often these metrics are part of the tool set used to perform the A/B testing.
The testing needs to produce enough usable data to make any measurements usable.