Monitoring Mode impact on V10000 G2 performance http://www.websense.com/content/support/library/appliance/tech_tips/v75/wsg_perf/config/webdlp_impact/first.aspx

Monitoring Mode Impact On V10000 G2 Performance

The Websense V10000 G2 v7.5.0 supports inspection of outbound traffic when that traffic is routed through the Websense Content Gateway module, and the WebDLP functionality is enabled and configured as "Monitoring" rather than "Blocking".