fran. I think the idea behind a draw in most areas is to allow for a controlled number of animals to be harvested. There is a population large enough to allow for some hunting but not enough animals for a general season. At one time point restrictions were the rule but since we've moved to a draw system the quality of bucks / bulls has went way up. Here's a site with info on the draws and priority (# of years) needed to draw a tag.
http://www.srd.gov.ab.ca/fw/hunting/2006Drawsreport.html