I always thought "I can just add another to the herd..." until, Tallulah bat hippo skinny pig! We have a happy herd of 6, all bonded and settled, then piggy daddy heard of a friend of a friend who had taken in 2 unwanted pregnant skinny pigs who had babies... Tallulah aged 8 weeks old attacked our boss lady and 2 of my other piggies, and they fought back, and within 5 minutes of attempted bonding I was phoning the emergency vet and mopping up pools of blood and ripped fur! Then Tallulah got an abscess from one of the bite wounds... and it all got very stressful and expensive and at one point almost fatal... and then, she was still on her own, and had to go dating, get her own cage and friend...
This was a big lesson for me in "but we have space for another in that big cage"- I now have 8 piggies, with Tallulah and Ollie living in their own cage, in a different room... once you need to do the "permanent plan B" (plus vet bills and worry after a serious fight, like snarling tigers they were!) it does rather dampen the urge for just one more