My Computer can get to be a little over-crowded very easily. When you plug-in a jump drive Windows will automatically assign that drive a letter somewhere between D and H. Well, let’s say you have a:
Floppy Drive (A)
Hard drive (C)
CD-Burner (D)
DVD-Burner (E)
Then you also have some mapped drives to server shares:
Group files (G)
Home directory (H)
That pretty much leaves F: for your jump drive. If you want to insert 2? Well, it’s not likely to map itself with the way Windows handles it or if it does, it will likely be mapped to G or H and be invisible since the network drive is already mapped there.
The easiest thing would be to re-map your drives to places later in the alphabet, like R and S. But, when these drives are scripted to map for you at logon, the letters have been referenced as such for years in documentation, and not to mention the shortcuts… it suddenly might not be the easiest thing.
Using the USB drive letter manager service, an additional service in the background will re-assign drive letters to inserted jump drives where they might conflict with network/mapped drives. Basically this increases the range for mapping drives beyond Windows and checks for conflict all in the background.