I have tie down loops welded to my frame rails, front and rear on my car. You can see them here just after the wheel tubs. I prefer to tie the car down like this so the suspension isn't moving, and shocks wearing out.
Like Jeff says, attaching to the frame pulls the car suspension down, so it doesn't bounce around as much (which can wear shocks).
When I bought my Daytona, the previous owner had frame loops on the front, but axle loops on the rear. He showed me how he used an extra strap on the parachute frame to pull the suspension down. Saving the shocks.
