Who is even buying 120gb or 240 gb drives?
It's not even about space actually.
Because sure you can boot a system off of 120gb no problem.
However testing by Tomshardware, Anandtech and others has shown that at the bottom end of the capacity range, the less chips on the PCB means lower throughput.
You really have to be at 480GB+ to start taking advantage of SSD speeds through a SATA III connection.
That, and the price difference between this and one of the excellent Samsung 2.5" SATA models is negligible.