Quick format on DVD-RW

Hi...
I've bought several DVD-RW for testing my creations. My question is I always do a full format after using them, will a quick format be the same? they've told me a quickie will not erase completely the data, is that true?

Also, what is a the average lifespan of a DVD-RW??? I know it depends on brands, but I'd like an estimate: 5 formats, 10 formats, 20 formats???

Thanks!