Software diagnostic tools are useful for diagnosing potential faults in a computer system.
This question is a bit vague, however, as there are a great many types of diagnostic software for dealing with many different systems and applications.
There are many things that can be diagnosed, such as databases, file integrity, computer operating system integrity and hardware like hard disk drives, network cards, graphics cards and RAM memory.
The right diagnostic tool can be very useful if you suspect that something is wrong with your computer, or certain applications on your computer, as this will help you determine the nature of the problem. Once this has been identified, then you can attempt to find a solution.