Guaracha dance is son dancing at a faster tempo and with a lighter, more playful attitude — the physical expression of Cuban popular music's great comedic tradition.
The guaracha is not a radically different dance from son — it uses the same basic step and partner framework. What changes is the quality and energy:
According to Wikipedia, the satirical guaracha lyrics suited son well, and many bands played both; EcuRed counts the guaracha-son among the variants of son. In practice, much "son" dancing in social settings is really dancing to guaracha-son: the grounded body movement of son with the faster tempo and comedic energy of guaracha.
When the music picks up speed and the singers start trading jokes and insults in the coro, the dance reflects it — lighter, faster, more expressive.
Guaracha spirit lives on in timba. The playful coro texts, the banter between singers, the teasing musical phrases — all of this invites a guaracha quality in the dance: responsive, light, a little cheeky. The dancer who can hear the music's humor and express it physically has understood something essential about Cuban dance.