We've talked about blow-off bottoms before. They happen to be my absolutely favorite kind of trade. First they are extremely obvious on just about any time frame, second, they can occur either on a gap up or a gap down (but more prevalent on gap downs) and third, they result in high probability trades. Here is CVNS - I've played this one before and did not play it today but I was looking through my watch lists after the market closed and this stood out like a sore thumb. This is being played on the 30 minute charts and note what happened with the 6th bar - it formed a high volume red hammer. Unfortunately I wasn't paying attention at the time and didn't see it.
The 30-minute charts provide slow developing set ups that, once established, will last for some time. While you could have picked this up from the 15-minute charts it is more crisp and obvious from the 30's. This is why many of our contemporaries prefer the 30-minute charts.