The plug in can be used to create a service functionality or any other functionality. The logger are specifically differentiated according to that.
Service plugin - like calling a service in fuse to validate the data entered by the user. The servicelogger is preferred here as compared to non service one.
https://www.ibm.com/support/knowledgecenter/SSEUEX_3.0.5/com.ibm.developingeuc.doc/eucso006.htm
nonservice plugin is used when no service is being called via the plugin.
The difference is nominal but when you use the nonservice logger in service plugin.. the logs are generated in a temp folder(not known location) which will increase the size of that drive and it will not be cleared off (like if service logger is used). This is what we faced recently and have to change the logger to service one..
thanks ..