There are viruses that make some plants look more appealing to some people. For example they are the cause of these striped patterns on tulip petals.

I assume you mean beneficial to humans?

Viruses make up a large portion of Earth’s ecosystem, and a large class of them help keep bacteria in check.

https://en.wikipedia.org/wiki/Bacteriophage

There are even efforts to try and harness them to treat bacterial infections.

https://en.wikipedia.org/wiki/Phage_therapy

Some viruses are useful for studying genes - you can make them transfer a genetic sequence into a cell.

They can be used in gene therapy - a very promising field of medicine.

And some viruses could also be used instead of antibiotics, which could potentialy solve the resistence problems and also help avoiding collateral damage to symbiotic bacteria. (Research of this technology is quite old, unfortunately it was abandoned for a long time and everyone focused on antibiotics instead.)

Viruses affect other things too, including bacteria! Bacteriophages are the first to come to mind

https://m.youtube.com/watch?v=SbvAaDN1bpE

Sorry to link to a video, but this recent Kurzgesagt video covered your question pretty closely :)

Probably, yeah. Their whole schtick is to move DNA around and fuck up genomes n shit. They’re evolutionary drivers.

There is the “Luck Virus” and “Sexual Magnetism Virus” poor Rimmer

https://www.youtube.com/watch?v=YI3tsmFsrOg

There are beneficial bacteriophages for humans and other animals and plants.