Vegas creates temp files and in normal uses, it deletes them when finished. That's why it is recommended to have at least 2X your approximate project size in available disk space.
However, if 3Gb is causing you pain, then you should be looking at a larger hard disk.
3 GB is a LOT of space to be wasting, for no good reason. These TMP files are often left behind when Vegas crashes. It is perfectly OK to remove them, and is actually a very good idea to remove them. In fact, it is generally a good idea to have a look at your TEMP folder from time to time. It is amazing how sloppy some programs are, and how much flotsam they leave behind.
I've had crashed galore with 11 and 10, but I've notice that Win7 64 appears to be jolly good at allowing Vegas to zap 'em. I used to be able to register at least 300mb of temps following a bunch of User induced crashes, now, as I said, not a sausage!