I would not say that judicial notice is a terribly important doctrine. Instead, I would say that it is more of a convenient doctrine. If there were no such doctrine, American legal proceedings would not be all that different. Therefore, it is not a very important doctrine.
Under the doctrine of judicial notice, a judge can essentially allow a fact of some sort to be used as evidence without requiring expert testimony to establish that fact. As this link tells us,
A judicially noticed fact must be one not subject to reasonable dispute in that it is either (1) generally known within the territorial jurisdiction of the trial court or (2) capable of accurate and ready determination by resort to sources whose accuracy cannot reasonably be questioned.
In other words, this has to be something that everyone knows or that can be proven very easily and beyond any reasonable question.
This is not a very important doctrine because, were it not for this doctrine, the facts at issue could still easily be proven. For example, let us say that for some reason it was important to establish that McDonald’s sells hamburgers that are not flame-broiled. If judicial notice were not allowed, it would be easy enough to get the manager of a McDonald’s to testify as to how their hamburgers are made. This means that the doctrine of judicial notice is not really all that important.
The doctrine is, however, convenient. It allows a fact to be established without (in this case) wasting a McDonald’s manager’s time by making them come and testify. It can make trials shorter and less tedious. Therefore, it is a convenient doctrine, but not a very important one.
While I think pohnpei397's definition and explanation of judicial notice are spot on, I feel it's important to point out that when it comes to court cases, convenience is importance. It is no small thing that a court does not have to worry about obtaining evidence or authority for every single piece of information. Judicial notice greatly impacts the amount of time spent in court. When we talk about facts submitted in court, that means every fact. "The most common judicially noticed facts include the location of streets, buildings, and geographic areas; periods of time; business customs; historical events; and federal, state, and INTERNATIONAL LAW." Imagine if during a court case, a man had to prove a street really existed where he said a street existed, or the year 1989 actually happened. Think about how many extra materials would need to be presented in court, along with all the extra people who would need to be brought in as voices of authority, were it not for the doctrine of judicial notice. It is a convenient doctrine, and convenience in court cases saves time and money, which is very important.