Imagine you want to make 10^9copies of a book chapter in a vast library containing 59,715 books. Well, you have to give the librarian the details of the chapter & book so that he can first find it & then copy it. The more accurate the information, the faster the document will be found.
This is precisely what primers do in DNA replication & polymerase chain reaction (PCR). PCR is the 2nd main method in the genetics studies, which has many applications in simple to advanced genetic research & various fields in biology. The more precise the primer designed for different types of PCR is, the more precisely it sticks to the beginning & the end of your target gene & generates copies better. If the primer design is wrong, we have to redesign the primer after spending time & money on primer synthesis & PCR.