What is RF switch used for in a lab equipment?
One place RF switches are used is to switch, or multiplex multiple RF sources into a single piece of test equipment.

Here's an example.  Most modern day antenna systems have multiple RF outputs that may include SUM, Delta-Az, and Delta-El channels.  All of these need to be characterized for phase and amplitude response as function of frequency, scan angle, temperature, etc.  These measurements are done using complicated/expensive test gear like spectrum analyzers and vector network analyzers (VNAs).  It is usually cost prohibited to provide one set of this test gear for each of the 3 channels mentioned earlier.  So it is very common to have a single set of test gear and an RF or set of RF switches that switch the desired RF channel into the test set to make the needed measurements for each channel.