Hello and welcome to the forum!
The Goa Carnival dates as far back as 500 years ago. Back when Goa was ruled by the Portuguese, they have this annual, four-day festival before the beginning of Lent season. It was a bit of a mockery at that time, where the "white" rulers become the slaves and the slaves plaster their faces with flour so they can exchange places. The local Konkanis would then watch this entertaining show.
You could say that before, there were traces of Portuguese signs and elements in the carnival. Nowadays, we'd see that it is more Goan in style and elements. With all the colours, from the streamers, to the ribbons, it has become an integral part of the Goan culture and pride.
It is said that the Goa Carnival is the most anticipated event in Goa. Preparations for the show start as early as December. It's not just music and dance that you'd see in the carnival, there's also plays and dramas depicting the tradition, culture and history of Goa.
The carnival usually starts on the Saturday before Ash Wednesday and can continue until Tuesday. It is recommended that you book in advance for tickets and for hotel accommodations as this is the time when tourists flock to Goa to witness the event.
I think it is worth it especially if you like festivities and events. Just seeing the giant floats and the parades are well worth the trip.
I hope this helps!