Difference in spool settings

The system is a Windows NT 4.0 with Services Pak 6a. When you go into properties of a printer, you'll see a scheduling tab. I was wondering what is the difference with "Print directly to the printer" and "Spool print documents so program finishes printing faster"? Does print directly mean that the computer will send as much data as possible to the printer memory until it's full. Then the remaining data will stay on the computer, but the computer will be slow or locked up till the remaining data is sent? Also what is the difference in priority? If it has the highest priority, does it mean that the document will print faster or what? Thanks for your help in advance.