Vehicle livery is very important for ambulances because it is a necessity that people can recognise them quickly and easily regardless of whether they are driving or not. The majority of these reasons are for the safety of everyone in and around an ambulance as they are likely to be driving very fast at the time.
Although an ambulance's siren is a pretty good indicator that one is approaching, there are still a number of different reasons why vehicle livery for the emergency service is important. Many people listen to their music loudly when driving in their cars which is undoubtedly going to limit to what they can hear happening around them. However, people look in their mirrors frequently when driving so even if someone has their music playing loudly and they can't hear the siren they will instantly be able to recognise an ambulance approaching them and therefore pull over to let it pass.
One of the most important reasons why people should be able to recognise that an ambulance is approaching them instantaneously is because it is very likely that the ambulance is on their way to an emergency situation. If a pedestrian or driver has not recognised that an ambulance is approaching them then this could delay and cause obstructions for the emergency service which could have drastic consequences. Vehicle livery can prevent this from happening because with the right design people will instantly be able to tell that an ambulance is getting closer and therefore ensure that they do not obstruct its path.
Ambulances may become a hazard to other road users when they are on their way somewhere and are driving very fast. For this reason it is imperative that motorists can see an ambulance coming from a safe distance away so they can be sure to slow down and pull over until it passes. If ambulances didn't have any vehicle livery people may struggle to recognise them until they are very close which may cause accidents as people suddenly break to slow down.
Vehicle livery is extremely important for ambulances and can even save lives. Although not all ambulances are identical and may vary depending which area you are in, their design makes them easy to recognise even if you've never seen that particular one before. If all ambulances looked significantly different then it would be difficult for the general public to recognise them approaching which may cause accidents and delays.