A software access point (SAP) is a computer with wireless NIC running software that enables it to function like an AP. Software access points can be sophisticated and may duplicate many of the features of a hardware AP. A PC acting as an SAP may suffer performance degradation if there is a lot of network traffic, because more of the CPU's resources are required to handle the duties of the AP.
The PC used as an SAP must remain running and available or
network clients will be unable to connect. If you are sharing an Internet connection, the computer acting as the SAP may have to run connection-sharing software (see the following section, "Secret #30: Sharing an Internet Connection via Software") to enable clients to connect to the Internet if the computer also is directly connected to the Internet. For best performance, a hardware AP is a better selection, but if you can't afford one or need a quick substitute, an SAP is a possibility. Even then, the PC running ICS software and sharing the Internet connection should be dedicated to that purpose for best performance.