Exactly what a light rider (as I was back when) needs to do after running out top gear on the descent.
To get the maximum advantage out of seconds gained on the climb it is imperative to carry momentum over the crest, shift to the big ring and spin out the gear range as efficiently as possible.
Listen/watch for the big guys coming up while recovering in an aero tuck (if they can close the gap) and grab a wheel to recover and launch onto the inevitable next climb: Repeat.

A decided advantage for light riders on technical descents is that they are on the same size tire and compound as larger and heavier riders.
The confident well practiced light rider can take tight lines, brake later and generally scare the willies out of the big guys with the finite amount of traction available to both.
Samuel Sánchez in the pro ranks at 143lbs is one of the finest descenders of the era: calm, confident and very fast.

https://www.youtube.com/watch?v=1WIvl2WiUEA

-Bandera