I have two, I use them as "see me" lights generally because I like the way they strobe. They're bright enough that when it's dark out, anything that is reflective, like road signs or reflective patches on other cyclists' clothing will light up like it's flashing neon or something. It's quite something to see...this little town near me called Nanaimo has this giant sign when you enter the city, something like "Welcome to Harbour City". It must be particularly reflective, because every time I ride there it just lights up, flashing like mad. The sign is huge, too.

They are also bright enough to help you see the road, although I wouldn't say this is their strength.