DDoS attacks can render sites unreachable or may leave you with a enormous bill to pay for traffic. Last year the security blog of the well known security expert Brian Krebs was dropped by Akamai after being hit by one of the largest DDoS attacks. Akamai didn't charge for the attack but if you are less fortunate it can get very expensive.
Google is offering free DDoS protection for certain pages (news, journalist, human rights and election monitoring sites) with their "Project Shield" service. If you fall into any of these categories you can apply for the free protection service.
Find out more at https://projectshield.withgoogle.com