As dogs get older or for some pets with mobility problems then a dog ramp can be helpful in getting you dog into and out of your vehicle, caravan or boat. Or for going into your home if it has steps.
A slight word of warning, we bought a good quality dog ramp for one of our dogs and found that he would not use it. Now a bit of patience and training may have helped and encouraged him to use the dog ramp for getting into the car, however another issue we had was the physical size of the ramp - it was difficult to carry about with us and it was very heavy. Now if you have a large 4x4 it probably will not be an issue, in our car it would have taken up too much space. We eventually gave the dog ramp away to a dog trainer friend to use with her dogs.
So before you go out and buy a dog ramp for your vehicle consider the size of the ramp and if it can be stored in the vehicle along with your dog(s), and secondly are you strong enough to physically carry and set up the ramp as some of the stronger ramps for larger dogs are fairly heavy.
Dog ramps can be a life saver if you buy the correct one that meets your dogs - and your own requirements.