Testing is a very important need. We are living in a Agile world, where there is continuous development,continuous deployment and for that testing also need to been done in a continuous manner. Testing make us sure the that product build is save and is proper functioning under different different circumstances.Testing is even needed to meet the audience requirement. There are several reasons to answer why testing is required. But in short i can just say is Testing for a software is very much important and is need to be done in a priority basis.
You can use LambdaTest for Cross-browser testing. As Ihave find it more useful in my personal experience.