Originally posted by wizard_of_woz:

Do the iron beams actually help support things?

A bit, yeah. They have a much higher stability score than most materials, so most other pieces will effectively treat them as a ground connection even when they're bright red, and a beam will stretch a good way when supported by a post at both ends. Horizontal support is non-intuitive but does exist, and pieces that would immediately collapse placed individually will hold together in an unbroken line mutually supporting each other. Try building with support poles, but then removing the middle ones after everything's in place.