Drilling, tapping, counterboring, and countersinking are the usual operations done in sheet metals.
Drilling: Drilling is done in sheet metal only when piercing cannot deliver the accuracy required. For example, on a formed part, when holes on different features need to be coaxial, the accuracy obtained by machining may be required.
Tapping: Tapping can be done using cut threads or formed threads. Formed threads (thread rolling) is preferable for the following reasons:
Counterboring: Counterboring is often done to provide clearance and a bearing surface for the fastener's head.
Countersinking: Countersinking allows for flush mounting of flat head fasteners. Countersinking cannot always be done for very thin stock or for very large fasteners.