Every PROFIBUS segment needs to be terminated properly and supplied with voltage. If the last station on the network has inactive termination on its connector or this connector isn't supplied with voltage (e.g. you tend to switch that station off), the quality of PROFIBUS signal on that segment can be affected and a network failure can occur.
You can prevent this by installing an active terminator. You take the last station and make it the last but one station on the network, bring the PROFIBUS cable out and connect it to an active terminator. You'll then get a properly terminated end of the segment as well as a service interface for connecting the ProfiTrace2 analyser.