That's fine on your local network. If you're pinging a system out of your local network, what you're doing is considered by many to be a denial of service attack.
It's not even close to the most effective denial of service attack, but if I were to do that from my 100 Mbps Internet line I could overwhelm many company's Internet lines with a simple ping flood.
Sure. I added "local" about a second after posting for this reason. However even with -f you can just specify an interval when running tests outside your lan.
http://en.wikipedia.org/wiki/Ping_flood
It's not even close to the most effective denial of service attack, but if I were to do that from my 100 Mbps Internet line I could overwhelm many company's Internet lines with a simple ping flood.