For replacing the glass, it has to be figured first how it will be taken out. Even though it is shattered into countless pieces, the glass would have to be removed from the edges before installing a new one. For a door glass, the door panel has to be removed to access the mechanism that moves the window up and down. The glass is attached below. The front window repair and rear window glass requires the trim and the rubber gasket to be removed. The rubber gasket has to be replaced with a new one as the new one is installed. The car manual will be of help for removing and replacing the glass.
If the crack looks exactly the same when completed, it's very likely the technician didn't inject the resin properly. A properly completed repair with cause each area of the damage to disappear from at least from one angle of vision (ex: looking from one side, looking from below, looking from above, etc.).
Why do you think there is windshield repair? You got it, cost. Some insurance companies want you to repair rather than replace because of cost. They save a fortune if you repair your windshield. Also, you need to check with your state as to what is legal as far as windshield repair all states have different laws regarding this issue.
Since the windshield is a safety precaution and a major area of your car it will need to be in excellent conditions. If you ever plan to sell or trade in your vehicle you will not get a full value or may even lose a sale if the windshield is not in good condition. It is not safe and it definitely does not fix auto glass repair look good!
One more thing to consider is the amount of things we can see through the windshield. If there is a difficulty in the driver's vision then it is common sense that there will be a higher risk of accident. Windshield plays a vital role in ensuring the driver's clear vision of the road. With that being said it answered the question why is it important to repair the windshield. It is very easy to find someone who can repair the windshield. All of whom are very competitive and knowledgeable so you don't have to worry.
Windshield cracks and blemishes can be troublesome. You can never really guess what is going to happen; they almost always start small and end up spider webbing across the remaining windshield. Some rock blemishes only leave chunk of glass missing. If not treated correctly it can turn into a large crack as well.
If you have a chip or a growing crack in your auto glass then the best time to get it taken care of is immediately. Every heavy gust of wind or debris that strikes your window can cause a large and sudden streak in a crack that forces it to spread. Tend to your windshield and get the crack taken care of immediately.