They disrupt your work and your environment.
They can corrupt your data and you lose work.
Denial of service attacks and prevent you from getting to services (yahoo, banking, google, etc.).
People's first thought is problems are caused by a virus to they try to fix it and waste time if the problem is somewhere else.
Disrupt business and commerce meaning loss of money to business and people
Overall, the biggest impact is the loss of time they cause to everyone. If you think of time as money then loss of time means loss of money.
Makes people scared to used online services. People lose the advantage of online services. Business providing the service don't get as many customers