The effect of switching logging on is that the service's request and response blocks are written to a diagnostics file each time the service is invoked. This file is stored in the server's system directory, which defaults to /var/mfcobol/es/es-name where es-name is the name of the enterprise server. The file is named casdumpa.rec (or it might be named casdumpb.rec if you specified a maximum diagnostics file size on the Edit Server page).
You can format and view the information from the Edit Server > Diagnostics > ES Console page. The client request is shown in a block named user-storage-type under the part of the dump entitled CAS-REQ. The server response is shown in a similar block under the title CAS-RESP.
Only switch logging on if you need diagnostics as it degrades performance.