SwitchClient is part of the Switch product but it has its own separate installer so that it can be easily deployed on several computers in the network.
There are no license keys for SwitchClient itself; what's licensed is the number of simultaneous connections to the Switch server.
More precisely, the Switch server keeps track of the number of distinct SwitchClient instances that logged on at least once during the last 30 minutes (not counting the SwitchClient instance on the same computer) and compares that number to the licensed number of connections.
A regular Switch license includes a license for up to five SwitchClient connections. Licenses for additional connections can be purchased separately (see purchasing Switch and contact us).
The license keys for additional client connections must be entered using the Switch client licensing dialog (not in SwitchClient).