Most points have been hit here. You can definitely save some money buying end of season leftovers, but I wouldn't let that drive your decision unless you are really hard up for cash (in which case you couldn't afford to snowboard anyway.)
You run the risk of many of the better boards and common sizes not being available. That said, if you do your homework and find gear that is suitable for you and can get a discount, go for it. Just don't let the discount drive your purchase since you won't notice the $ as much as you'll notice riding a board that isn't right for you.