One interesting side effect of having a legitimately fast SSD is even though you save power power on not spinning a platter around you can end up using that power (or more) with increased CPU usage. Ex: Semi-Random reads from mechanical drive might be pulling data ~40MB/sec on a good day... the CPU doesn't have a lot to process at once or just does in chunks so all that nice power saving tech comes into play (reduced clock or cores or what have you). Now, pop an SSD in and start getting 300-500MB+ semi-random read speeds and your CPU will find itself a hell of a lot more busy having to actually process all of that.
It's a good "problem" to have, if you can even call it a problem
If you need to read 1GB of data off disk (say, loading a game or something) wouldn't you use exactly the same amount of CPU power whether you load it at 40MB/s or 400MB/s? Either way all of that data needs reading from storage and 'processing', why does reading it slower mean it takes less power?
If anything I would've thought and SSD takes less power overall because you can wake up the full CPU, do any processing and then put it back into a low-power mode. If you're streaming data slowly you need to keep at least 1 core active to handle the stream.