Arnie said do it (although I don't think he did it all the time himself), so I did it for the vast majority of my training career. It makes sense that greater effort results in more muscular hypertrophy. It seems that for strength, failure is a no-no, though, which I've really just learned this past year. Ed Coan said he avoids it like the plague. Some of the most impressive gains (to me) that I've ever made on bench press were using a Coan periodization scheme where failure was not a necessity. I say mix it up a little, but back off sometimes. It depends on your goals as well, of course.