Answer: The Gemara (Eruvin 65a) teaches that there is a special beracha given to a house in which wine is spilled. Following this, the Rema (OC 296:1) writes that we pour some wine out after havdala and extinguish the light in it in order to start the week off with a siman beracha.
The Taz (296:1) writes however, that pouring out wine in such a way would be wasteful and considered a disgrace. Rather, the Gemara means that one should fill one’s cup to the brim, even allowing it to overfill a little. He explains that the Gemara doesn’t ask for one to pour out some wine, but teaches us that one who does not become angry when wine is spilled in their home, will be blessed.
The Shulchan Aruch Harav (OC 296:5) writes that it isn’t disrespectful to overfill the cup as one is only wasting a little bit. After drinking some of the wine, one should pour out a little of wine to extinguish the havdala candle to demonstrate that one only lit it in order to perform the mitzva of havdala.
In conclusion, while one mustn’t purposely waste any wine, it is commendable to overfill one’s havdala cup slightly and to extinguish the candle in the wine.