Two components Fifteen Watts (update 11-20-2020)

(The new and improved UFO Drip is claimed to be 15% faster and 40% less expensive. Check it out.)

It's possible to gain up to fifteen watts with a clean chain, the right lubricant, and switching to latex tubes. Going from a dirty chain to the cleanest chain possible can save up to six watts. There are chain cleaning tools and ultrasonic cleaners that do a much better job than a rag.

There is a five watt different the best and worst chain lubricant. The best chain lube is UFO Dripand is very expensive. I use the second best which is Squirt and is very inexpensive. 

Depending on your tire pressure (more on proper tire pressure here) you can save three to four watts using latex tubes instead of butyl rubber with continental gran prix 5000 tires (the best rolling/puncture resistant tires in my opinion). Latex tubes are no less puncture resistant than butyl. Check this site out for this information and all different types of tires.

6 watts clean chain + 5 watts right lube + 4 watts latex tubes = 15 watts

Say you aren't starting in the worst case scenario and you saved 10 watts. Ten watts can save you 1 second every kilometer. In a 40 kilometer time trial you could be 40 seconds faster. And this is only focusing on your chain and tubes. A while back this was enough for me to start taking these details seriously.