ActionableMango hit the spot, you don't have to defend the method you choose, I posted that question because I am getting a SSD and would like to understand why you chose to have it in the enclosure.
I will be using the SSD for the OS, and I prefer to have it internally, and I suppose the speed gain is best when inside. The HDD is going to an external USB3 enclosure.
Well, I suppose if you are going to go to the trouble of disassembling your Mini to install and/or remove a drive, then you might as well put the SSD in internally and put the hard drive in an enclosure.
For me, there isn't really a disadvantage to just plugging in the SSD externally. Also I have the benefit that if I decide to take my Mini anywhere, the hard drive is installed internally and partitioned such that I can use normally...