Buying a category S car is one that has suffered structural damage and has been written off as a result, but that may be repaired and returned to the road. Whether it is a sensible buy or not depends on a number of factors. If you plan to repair the car yourself, this could mean a bargain based on the value of the car before it was damaged, but it is essential that any repairs are carried out to the required standard. The car will have a category S marker forever, so its resale value will be reduced and the cost of insuring it will also be greater than an equivalent non-cat S car.