The place where lighter rims/tires can make a real difference is mass start road racing. If lighter wheels means just once, you make the split instead of coming 2 feet short, that could mean being in the winning move, minutes ahead and many places at the finish.
As a small engined racer, I was a big fan of light rims and tires. Races Fiamme Ergal rims (290g) and Criterium Seta sewups (250g), sometimes the matte thread version @ 220g. Spokes that were the equivalent if DT Revolutions weight-wise.
Ben