Seems like I wait much longer than others. I have about a 5 yr split between dogs. That way I am better able to raise and make each be 'all that they can be' as individuals before adding another pup (and a TIME SUCKING pup) to the mix.
I spend so much time socializing one puppy the first year, and training that year and the following. And really developing their individual personalities so I know my dogs as individuals (rather than the pack). And it's vital to do all the separate stuff, taking the new puppy away from the house/other dogs, car rides, training, visiting friends, relatives, etc. Otherwise the dogs will become 'doggy' and much more attuned to each other while the humans are just periferal to their lives giving food and petting but not needed for anything else.
I have such high hopes and expectations from each of my dogs, and want to KNOW that I have done my best before adding another and forcing my attention from the older dog and onto the new one. My guilt is much less when I know the older has had their time with me.
I want dogs that all my friends, neighbors, relatives, coworkers know and love. So that I never have to kennel them but always can either bring them with me on all vacations or have a literal waiting list of people who know and love them. My dogs get along with other dogs and that's what I expect. They get along with people and have their CGC's and that's what I EXPECT.
Something else people never think of when adding more adorable puppies to the house, is 12 -15 yrs down the line when the dogs ALL BECOME SENIORS at the same time. The cost of this. Stress and worries of this. Vet visits. Issues with incontinence, having to assist carry a 75 plus pound dog to get them outside or back on their feet if they stumble....... Think it's much more responsible to ourselves as well as our beloved pets to deal with only one of these senior dogs at a time.