Advantages

Power efficiency. Use less electricity
Higher performing. Brighter
Long Lasting. Replace bulbs less frequently
Safer. Indicators and stop lamps activate more quickly thus alerting following drivers
Style. More possibilities allowed, such as built-in sequential turn signal animation
Space-saving is possible
Less heat generated, so interior bulbs do not damage the lenses

	LED	Incandescent
Environment/Power-saving	0.2 W	5 W
Safety/Response	2ms (equal to a distance of 0.05m when driving at 100km/h)	300ms (equal to a distance of 9m when driving at 100km/h)
Maintenance/Long Life	over 3,000 hours	500 hours

source: Koito☁

Disadvantages

Price. LED bulbs usually have a greater initial cost than incandescent bulbs. However, this is offset long-term by the longer life
Selection. Very confusing as to specs, performance and quality

LEDs get darker than incandescents, so remember to replace them long before they burn out.

Incandescent 2000 hours  7% loss
CFL         10000 hours 22% loss
LED         20000 hours 30% loss

Early LED tail lights used many small bulbs to replace a single incandescent bulb, resulting in a "spotty" look.

1st Gen	Multiple spots of light separate reflector
2nd Gen	Smooth look integrated reflector
3rd Gen	Advanced look multiple accent features