If you use a rate that you are not eligible for its screws the ppl who are entitled to use that rate, if you take the last room available at that rate.

Also, it has been explained that too many people using a corporate rate actually hurts the company. For example, a given hotel manager might decide that to meet his nightly occupancy levels he needs to sell 5 more rooms on average per night. He might be willing to extend a discount to a company that needs 5 rooms per night. HOwever, he won't extend that special if the company needs 9 rooms per night on average because those extra 4 rooms would be sold at a higher rate.