Many people have doors that have windows, or doors that are completely made out of glass, and only the frames are made out of wood or metal. This is an aesthetic addition to ones hallway and it also makes it lighter because of the natural light that is allowed to flow in through the door. The problem is that when there is light that can enter, also unwanted people can see in your home, and maybe even make decisions that can affect your security. This is why you should have front door window blinds.
If your house is easily seen from the road traveling past it, there can be people who you do not know that are trying to look inside your home. They are not necessarily trying to have a look at how good looking is your interior design, but they want to know whether there is something valuable that they could steal. This is why it is important to keep the windows covered with curtains or blinds, and it is preferred to have both, when you are not in the house. If you get adjustable window blinds you can use them when you are in, to allow light to come in and to prevent people from seeing in.
For doors it is as important as for the windows, since it is normal for someone to be standing in front of your street door. No-one would consider it being suspicious if someone is standing there, but if they were looking inside your living room window, it would raise some questions. That is why it is important to have door window blinds if you have a door that is made out of glass.