Reading through some articles this week, I found a link to a http://www.fangraphs.com/community/what-is-more-important-for-a-fastball-velocity-location-or-movement-2/
You hear so much about how a fastball is straight as it's a negative thing. It's quite relevant right now to Astros fans with all these discussions about the struggles of Mark Appel.
We also hear about how a pitcher has plus velocity, or above-average, or below-average, or whatever description is used based on the 20-80 scouting scale.
Then there's talk about how well a pitcher can locate a fastball. Another topic that surrounds the Appel situation.
However, rarely is there a discussion about which ones are more important than the next. That probably has a lot to do with each being a little more important than the other for each different pitcher.
However, the study is quite interesting in how it shows that location is more important in terms of swinging strikes vs. home runs.
There are limitations to this study though. It only differentiates between swinging strike and home runs. This doesn't discuss batting average or differentiate between other batted ball types.
That said, it does seem that the general idea of straight fastballs lead to more home runs is not as true as believed. Perhaps Appel's struggles are more related to his command.