Well, I realise about installing XP and re-installing programs. But, just for the sake of the discussion, I reckon there are some advantages to multiple partitions.
More to the point, none of this gets me any closer to liberating my "inaccessible" 40Gb, which I want back! Anybody know how I can liberate my hard drive?
Anyway - for the sake of discussion - the (debatable) advantages of multiple partitions are:
1.) Using multiple partitions makes backups of data easier and quicker. Just backup the complete data partition.
2.) By putting all the temp files ( cache, tmp temp virtual memory ) in a partition, you can also clean all of them off the drive all at once.
3.) By having all your system files on one partititon, and everything else in other partitions, you minimise the frequency with which you write to the system partitition - the old human error thing - bad installs, etc.
4.) The obvious point of smaller cluster sizes.
5.) The system partition will require defragging a lot less often, in fact the only partition I defrag regularly is the one where I store all my files - downloads, music, video, all that sort of stuff. Oh, and the partition with the games on it, of course...
6.) I can store an exact image of my C: drive on a CD, which is useful were I ever to have a catastrophic failure. XP installs a lot quicker if you are accessing the hard drive rather than the OS install CD.
7.) Having a separate partition for the Swap File, prevents that partition from getting fragmented, which will slow Windows down. Set the swap file to have the same min and max size, then make it the first file on the drive. This locks your swapfile to an exact size, puts it on the outer edge of the harddrive which is the fastest access and reading, and since it is locked in size it can't ever fragment.
8.) I find multiple partitions easier to handle from a security point of view - I keep all my data directories on one partititon.
9.) Defrags are quicker.
10.) And finally... having a second, working install of XP on a separate partition, has saved my bacon on several occasions.
YMMV of course...