Should an I.T. Manager Have Purchasing Power?

By Purchasing Power, I mean if they should have the power (within reason), to purchase the necessary I.T. equipment for their department to function as well as for the company.

Examples of equipment are:
Backup storage media, be it hard drives or whole machines or UPS devices.
Printers and accessories.
Networking equipment.

Of course they should be able if asked to justify these purchases.