What is the most effective type of discovery in law practice?

The answer below pertains to a criminal trial and the law practice defending the defendant.

In the courtroom, the most effective type of discovery evidence is evidence that places the defendant in another location at the time of the crime. If the prosecution, as an example, has a 7-11 store video tape that shows the defendant at that store while the crime is being committed a long distance away, it is very effective.

Under law the prosecution must provide all such evidence or any other exculpatory evidence to the defensive