Most car insurance policies will cover only one vehicle. This is the vehicle that is licensed to be driven by certain people with specified security measures. People then get into a comfort zone with their insurance, and do not even think about whether they will be protected should they drive another vehicle for a day.
Sometimes there is a need for driving rental cars, such as when one is visiting a different city or country, or if their own vehicle has been taken in for a service. It has to be taken into consideration that there is always the possibility of an accident occurring on your travels, and that being on holiday or a business trip does not make you immune to the dangers of the road. A lot of car rental companies will include insurance for the vehicle in the cost of the rental. If you are renting a car, ensure that there is car insurance included in the rental agreement, if not, ask for it. The last thing you want is to be responsible to pay for the damages to a few scratches, or something more serious. Paying a small extra fee on your daily rental price can go a long way in giving you peace of mind and protection should anything happen. This could also be relevant if you are given a hired car for the day when your own vehicle is in for a service or repairs. In this case the people may not include insurance on the vehicle. It is a good idea to check any paperwork and ensure you are covered.
There is another instance when you could need car insurance for a day. What happens if you are borrowing a friend or colleagues vehicle for a few days whilst yours is being serviced or repaired? In most cases there will be designated drivers written onto the insurance policy, and in the event of an accident you would not be covered under that policy. It could cost you more than you could afford rather than just finding out from your insurance company whether you would be covered in the case of an accident and possibly even taking out extra cover for that day.