Another reason to use a snatch block is that it requires you to have a greater length of cable off the winch spool, thereby increasing the pulling power of the winch. On the Warn M12000, there are five layers of cable, and each time you go to a lower layer (always leave one layer on the spool), you increase the winches pulling power until you reach it's rating, which is with one layer of cable on the spool.
You can view the specs at;
http://www.warn.com/truck/winches/src/M1200.shtml
Note; Warn has a typo on the 12V DC Performance Specs, one layer has 12000Lbs pull, not 1200Lbs.
John K.