Usually we connect two san switches using fiber optical cable, the link or connection between two switches we call it as ISL(inter switch link), without trunking there will be no load balancing between isls, for example isl1 port sending 2g data, isl2 port sending 4gb data, after completing it's task isl1 port doesn't share isl2 port load because there is no trunking, we need to enable trunking on isl ports on both switches.
Trunking in brocade meant for load balancing, but in cisco it has differenet meaning for trunking there is a portchannel concept is there for load balancing between isls
I gave this based on SAN switches.