|They can be useful providing you can get the necessary information that allows you to interpret what is happening.|
The LED will outpost various codes as the BIOS goes through the POST and initialisation. The code it stops on will give you an indication as to which part of the process it failed on.
You need to be able to get the codes from the motherboard manufacture for your particular motherboard.
I don't think the one that is in the image will fit a laptop though. It looks as if it is designed for a PCI bus.