How important is a confession in cases with limited evidence?

In a lot of cases all investigators have is a small amount of evidence that points towards a certain suspect. In cases where the evidence is very limited how important is a confession to proceed with filing charges. For instance, you find the murder weapon with prints on it that match a suspect. All the evidence that is present is the prints. The prints alone is good enough for PC and arrest, but probably not enough to hold a conviction in court. Or even in a robbery or burglary all the investigatior have is some form of physical evidence that puts a suspect at a scene. The evidence is enough again for PC, but more then likely not enough to go any further. All you really have is weak cirstantial evidence that places a person at the scene or in possession of the weapon at one time. So, in cases like these how important is a confession to file charges?