When I was a juror about 1 in 4 cases were dismissed within minutes. Perhaps it was a bad week for the CPS in my area but it must have cost hundreds of thousands of pounds in legal aid, delays in hearing other cases, juror's time etc. to bring the cases to court. Multiply this cost by the number of courts in the country and millions upon millions of pounds are being wasted.
Another problem with bringing hopeless cases to court is the effect this has on the defendant. The poor defendant has to go through months of waiting for their appearance in court, living in fear of lost reputation, prison and fines only to be told that there was never a case against them in the first place.