The point is, with a manual SSD/HDD setup, you have a CHOICE. I personally install MS Office on my normal HD, but if I'd LIKE to, I could install it on my SSD. For me personally, I don't care if MS Word takes 2 seconds to load vs 1. The point is I have a choice. Fusion drive is the exact same physical setup as the typical manual config-- an SSD with a seperate hard disk, except you no longer have the choice of what goes where, the superduper Apple algorithm decides for you. Don't touch your photoshop for a few days? Well now it just got moved to your normal HDD. In exchange for not having to think for yourself, you get an overall experience that is somewhere in between a pure SSD and HD. The experience even becomes a larger and larger compromise as you add storage beyond the capacity of the 128gb SSD drive, as now the algorithm has a far more difficult time figuring out what to put where. If your computer is just an appliance to you and you don't want to make any conscious choices in how you organize data at the expense of optimzied performance, fusion drive is great.
http://www.anandtech.com/show/6679/a...fusion-drive/7
This technology has been around for quite some time in the Enterprise SAN arena. One of the big "selling points" at a certain point was "intelligent storage"- -which is exactly what the superduper apple algorithm is. The SAN vedors stated that the SAN would "intelligently" move data between SSD, 15K, 10K, and Sata drives based on data usage patterns. The days of manually deciding what data to put where, only to have it sit on "fast" disk space when unused would be a thing of the past. It will move this unused data to slower storage, thereby saving you $$$. Unfortunately, "intelligent" wasn't as intelligent as a human.. That file share you initially put on SATA that you kicked off an indexing job on one day? Well shit now you have a terabyte of word/ppt docs sitting in your 15k stack. Most people ended turning this feature off and going back to managing storage allocation manually.