Can viruses be beneficial?

In the past few years, with the Covid-19 outbreak, it is hard to imagine viruses can beneficial. But that is the reality and truth.
Yes, viruses can be fatal, but some viruses can in fact be life-sustaining. The SARS-CoV-2 virus has killed large numbers of people during the current pandemic.
But humans wouldn’t exist without viruses. How can they benefit us? Viruses aren’t living beings, yet they have had a great influence on evolution. Some viral elements have embedded themselves into the human genome and reproduce along with us – so-called endogenous retroviruses.
One type of virus helps form the placenta, for example, while other viruses attack harmful bacteria. Viruses also maintain balance in marine ecosystems, curbing the growth of algae and attacking bacteria that are harmful to sea animals.
Soon, viruses may even replace antibiotics in fish farming. Thousands of viruses have already been sequenced, including Ebola, Zika and bird flu.