Mrwurm - Now that everybody else has done such an excellent job of convincing you to tie your equipment down, I'll tell you about an incident I saw once: I was following a low-boy with a big Cat bulldozer on it around an Interstate cloverleaf, and when the trailer hit a really rough spot in the road, the trailer dropped out from underneath the 'dozer, and as the trailer went around the ramp, the 'dozer kept going straight. Fortunately, it was still over the trailer when they made contact again, but it had shifted toward one side a bit. I hailed the driver on the CB and let him know what had happened. He stopped immediately and chained it down. Somebody else had loaded it, he said, and he forgot to check.
I used to occasionally haul equipment short distances without tying it down, but not after seeing that.