While there are some dangers connected to using circumstantial evidence, this sort of evidence can be extremely important in proving criminal cases. If only direct evidence were admissible in court, there would be more chances for justice to be subverted.
Circumstantial evidence is evidence that does not directly prove that a particular crime has been committed. It is evidence that only lets us infer that a crime has been committed and that a given person has committed that crime. This is why there is a danger in this sort of evidence. We can misinterpret evidence and make incorrect inferences based on that evidence. However, it is still an important kind of evidence and should still be admissible.
The reason for this is that circumstantial evidence point strongly towards a person’s guilt or innocence and should therefore be considered. Imagine, for example, that I am suspected of stealing money from the company where I work. If no one has seen me do it and circumstantial evidence is not admissible, I cannot be caught. But think of the sorts of circumstantial evidence that could indicate my guilt very strongly. Imagine that I was the only one with a key to the place where the money was kept who was in the building when it was stolen. Imagine that I suddenly start buying a lot of expensive stuff the week after the money is stolen. That kind of evidence absolutely should be admissible because it strongly implies that I stole the money.
Of course, this sort of evidence can be misinterpreted. However, that does not mean we should not be able to use it at all. Instead, we should be able to use circumstantial evidence, but juries should be very careful about what they infer from that evidence.
While it should be admissable, it shouldn't be enough to confirm guilt. Detectives and private investigators may very well use it initially to determine possible suspects to investigate. But, without more direct evidence, it may be admissable to court, but it shouldn't be enough to convict.