Replacing optical drive in macbook with SSD: does it matter where the SSD drive is installed? I've just replaced my MacBook Pro's optical drive with an SSD. I used OWC's Data Doubler kit. I've moved my OS and all my data onto the SSD, and I'm now using it as my boot volume. 

In other threads, some people have swapped the positions of the drives, so that the HDD is installed where the optical drive was, and the SSD is installed at the HDD's original location.

Is there any good reason to do this?  Does it matter where the SSD drive is installed? In particular, would this configuration have any impact on battery life?
Yes this does matter depending on the sata speed of your hdd, ssd and the laptop.

My 2011 MacBook Pro supports 6 Gb/s to the original hdd and 3 to the Optical drive.

My ssd supports 6 Gb/s and my original hdd supports 3 gb/s.

Obviously, I did not put the ssd in the optical bay caddy (which would have been less work). Instead, I moved the original hdd to the caddy an placed the ssd where the hdd originally used to be.

This way, my ssd runs at 6gb/s and my hdd (still) at 3 Gb/s.

Good luck!