I saw one reference that discussed massed heavy machine gun fire being used in front of walking artillery barrages to attempt to catch enemy troops in the open as they unassed front-lline trenches in order to get out from under the worst of it. Also discussed using same in the interdiction role to prevent reinforcement and/or resupply of front line trenches. The below website has some histoical info on the British Machinegun Corps of WWI and references these tactics.
http://www.1914-1918.net/mgc.htm