I drove a recovery truck for several years, and can't help looking at loaded cars and motorbikes:
lots of people seem to think that one 25mm ratchet strap over the seat of a bike on the side stand is good enough. It isn't, and that's assuming you don't break the frame lugs. Yes, I have seen that on a six week old aluminium frame BMW that the previous driver had managed.
I once asked a driver in a motorway filling station what was holding the car to his trailer, and he looked at me as if I was mad and said the handbrake!!
Cars are strapped by the wheels not the bodywork. That's all four wheels. Don't cross the straps, and definitely don't use the same tie down for the middle…. Ensure the ends of the straps can't wave around in the wind. Slacken the winch cable. If you care about the paintwork, don't use your car cover no matter how well it fits.
The driver is legally responsible for the load, so if somebody else loaded your roof rack/trailer/etc, check before you drive off.
Bike racks can be very flimsy, and the straps that use a sprung flap to keep the tension worry me.
If you're following a vehicle with a loose load, drop back or overtake so it's not your problem. Although that won't help when a propshaft comes off the truck in front and punches through your floor. That was a BMW that my boss hadn't intended to buy.