Often, this comes about as the family thinks the dog really would love companionship (and often they would.... but...sometimes families ask about this when the current dog does -not- like other dogs!). And that can be true. But.... a second dog is not a good babysitter for the current dog.
One of the things I bring up, besides the time, money, energy, etc.... is to consider age. A one year old and a puppy. A two year old and a puppy. A six month old and a puppy. All will result in, ten years from now, having two senior dogs. Multiple senior dogs can be emotionally and financially draining.
When Blaze was three, I got Luna. He seemed to be very much an adult. And impossible to train.... I desperately wanted a dog who could (and would) do things. Now, looking back, I can't believe all of the things I taught him in that time period and everything he learned to do in three short years.
When Luna was four (and Blaze seven), I got Griffin. The four years is a better age gap, and again, she seemed fairly proficient at that point.
Griffin is now three. There is -no- way I'm ready for another dog, and likely won't be for several years. In comparison to what Luna and Blaze were doing at this point, Griffin seems to have no training! I recognize that he's more proficient at what he knows, that he has a higher level of precision than they ever will.... but it's just odd to think about.
Last year I did some board and training with golden puppies and while they sure made Griffin seem grown up, I do -not- want another puppy of my own for a long time!