Driving takes lots of concentration and planning.
To ensure you remain safe your eyes need to be constantly scanning the road in all the areas as shown.
By having a "fixed focal point" you put yourself and others at risk, and will only be capable of dealing with items within that fixed area.
By varying your view up and down the road ahead, your brain will take in relevant information and allow you to deal with that information.
Things that move will catch your eye much quicker than stationary items.
Moving items are a greater danger to you and you can act accordingly to whatever that may be.
By varying your focal points, it will also allow you to deal with the path of the road ahead as well.
Drivers who only focus at the very front of the car or just at the vehicle ahead of them will find that they are constantly having to correct their steering.
Drivers who only focus in the early planning area risk missing instant danger such as a child or dog running into the road, or maybe a parked vehicles door opening.
By Planning ahead it will allow you to deal with what is coming up, whether that be a junction on your left or right, Traffic lights, Roundabouts, change of speed zones, someone getting into or out of their car, someone wanting to cross the road, and many other things.
If you don't plan ahead you will miss these things, possibly be going to fast and be in the wrong gear to be able to cope with them safely.
Imagine you are driving along the road and need to take a junction on the left or right that is coming up, however, you are only focusing on the vehicle just ahead of you. By the time you get to the junction you will not have seen that there may be pedestrians waiting to cross the road at that junction.
Because of this, it is highly likely that your approach speed will be too fast to stop in time to let those pedestrians cross.
The Highway code changes now make it that the most vulnerable road users have more priority than those of us in metal boxes, therefore if it is safe to do so we should stop to let pedestrians cross at junctions. But if you were not scanning the road ahead you would never know they were there until the last second.
Hitting the brakes hard to let them cross could cause you to have a rear end shunt from the vehicle behind you.
If however you were paying attention, and scanning the road ahead well in advance of the turning, you will have had enough time to reduce your speed earlier to slow down following traffic so that the pedestrians can cross safely and you reduce any risk of having a rear end shunt.
Always remember, all vehicles that are behind you, make YOU the lead car. It doesn't matter how many vehicles in front of you there are, you cannot control their speed, but you can control the speed of everything behind you. Use that to your advantage to allow for extra safety to the more vulnerable.