I used to work as a grip in Hollywood and I worked on several blockbuster projects in the early 90s. We employed what seemed to be a small army of riggers to help with every aspect of the production. Seriously, there must have been at least 50 of these guys on set at any given time.
On projects of this scale, everything is big, heavy and temporary. Huge sets would be there one day and gone the next. Multiple truckloads of equipment and machinery were used every day. Moving all this stuff around was the job of the riggers and it was no small task. Without those guys the movies would have never gotten made.