You can erase it safely, even you can create a script that erases it everytime you launch planeshift.
Search pssclient.txt with the search engine, I remember that Seytra wrote how to do it.
Anyway, you can choose to delete it every now and then, it\'s safe to do it; after launching the client, another file will be generated.
It keeps information of what is load and also messages that help the developers to know where an error occurred and why.