It does improve performance by storing program launch data which RAM does not, or which is cleared when not needed, or via system powerdown.
The simplified results of those few tests that were performed have been used by every website since, and its rubbish (Google it and 99% will tell you it offers no performance increase, few have actually tried it), totally misleading.
I've tested myself using Windows 7 (x64), 9 GB DDR3 (only ever reached about 6 GB in use) and a 16 GB Sandisk micro SD card.
The speed programs launched improved drastically, from 3-5 seconds to under 1.
That's where the performance gains are, and that's why it was created.
Tt will not give read or write performance increases for other files a program might use, it is dedicated to program launch.
It always seemed to me to be sort of a kludge. If you want your applications to start up fast, put them on a SSD.
I did, a small cost effective one :) we all know a 128 GB SSD is not enough for windows over a couple of years use, what with program updates and installations, anything over that has scandalous prices.
Not to mention the serious bugs that have sprung up with a whole host of SSDs.
16 GB card cost around $15 at the time, much more affordable option.