aside from the obvious that only a certain percentage will claim the rebate. It allows the manufacturer to pass on a price reduction directly to the consumer rather than giving the retailer a price cut which they may pocket the difference. It gives them the ability to "discount" one particular line without negatively affecting the price of their other lines e.g. if they dropped the price of one model by $100 then effectively the other models look $100 overpriced but if they offer a cash rebate then they can keep the prices up for the other models (its one of those weird marketing things). It helps cashflow as the rebates can often take time to process and they have the use of the money until its paid out (I waited 5 months for a $200 rebate from HP). If timed correctly there's some accounting advantages as well. There's marketing information to be had. I've probably missed a few others.

Certainly, the consumer can take advantage of these by combining them with other retailer offers. E.g. Brother often do a $30 rebate on a label maker. The Warehouse Stationary have their coupon sales on a regular basis where you can get 40% off one item under $50. There's a brother label maker which sells for $50 less 40% = $30 less $30 rebate = FREE (yes this does work as I've done it a few times now).

Another example is Norton's $40 rebate on Nortons AV 2007. RRP is $40 so essentially its free however if you combine it with a DSE VIP card you get it for 10% less or $36. Basically they pay you $4 and give you the product.