There are many reasons to connect or add a second touch monitor on windows seven, or indeed add a third!
Reason one is that multi touch monitors go down in price the larger they are! So a 22"inch monitor can be had for a reasonable £200.
Reason two is the more glass you have on your desk, the easier it is to work. One of the earliest advocates of this principle was Terence David John Pratchett aka Terry Pratchett the Disc world series author and unfortunately one of the most prominent sufferers of Alzheimer's. As he said some years ago when asked why he had the screens on his desk, he replied because he could not get 4. When a few years later he managed (I believe) six screens, the response was because he could not get 8.
Some mobile emulators support multi-touch: notably Windows phone 7. Window 8 metro is definitely Multi-touch and to be at the leading edge is definitely towards cool.
The idea of having a test tablet PC for the just the cost of the (added) monitor is also quite appealing to anyone of a frugal nature.
It took about a day of hitting Google quite hard and also the excellent support from Novatech who supplied the monitor (there's a link in the article). There is a fair amount of misdirection on what can and can't be done so if you want to have a 2nd touch monitor and save yourself some trouble then click here…