LEDs are no good for GI - the main reason is that they are too directional and for GI you need a more generous spread of light. The opposite is true of inserts however where ideally the light is more directional or focused onto the insert. LEDs can bring out the 'true' colour of an insert. The pic below shows the lower section of my BSD before and after using LEDs. I never realised that the inserts were in fact purple! The lamps made the inserts look red because the lamp is actually a bit yellow itself. Using white LEDs the true insert colour can be seen. Another pic shows the insert in question looking from the bottom of the PF up into natural light.
The last pic is a perfect example of using LEDs to highlight a feature. I have used 10mm LEDs behind the headlights in the backbox of Getaway HSII and the difference is really amazing. the lamps light up the entire headlight area but the LEDs correct this with light axactly where you need it.