We have fostered cats and dogs (and various other strange beasts) for about the last ten years, probably a bit more. My most recent foster was a failure on my part, but there is a reason... I will get back to that in a minute. Anyway, when you begin fostering, you need to realize that not every critter and person will bond as well as others do. When you have fostered somebody back to health and they are ready to go, hopefully you will be able to meet the prospective adopters, and help to figure out what exactly that particular critter needs in a forever home- ie. kids vs no kids, only pet vs houseful of furry siblings, etc. And with you having spent so much time with the foster, you will know them better than anyone, which would help with placement- s/he likes this or that, eats this brand of food better, likes to lay in the sun in the afternoon, etc. All the important stuff, when it comes to fitting in with a new family.
Now, back to my most recent foster/failure... I have had dozens of foster dogs in my home and heart for many years. In some ways, I bonded with each one, but also knew that they would be moving on, and needed training, etc. before being placed. I had no problem letting them go to their new homes, because I knew there were many more out there in need of that level of care, and if I kept the current one, I would not be able to help the others who so desperately needed a second chance at life, and most likely they would have been PTS for lack of space/foster homes. My most recent foster, Jesse, is the first foster we have taken in in about 2 years, due to my health issues, and the fact that we now have two mastiffs. We knew our next dog would be a male brindle mastiff, and we were actively looking for one. When I got the call about Jesse, the understanding at the time was that we would do what we could for him, and had the option to keep him if he turned out to be what we wanted in a male mastiff. If we didn't bond with him, his personality didn't fit with the girls, or any of a million other factors, I would be responsible for his placement, as I would be the one who knows him and his needs and personality. So, we picked him up, as a small bundle of skin and bones curled into a ball and shaking like a leaf, afraid of everyone and everything, and brought him home. When he finally started to trust us, and started to come out of his shell, he blossomed into a wonderful pup who just needed training, food, love, food, and love and more food. He gets along well with my girls, he wants to be with us all the time, no matter where we are or what we are doing, and he is just totally a wonderful boy. He has the energy and drive to join agility classes, and the intelligence to join hubby in SAR training. I honestly don't think he would do well in another home, as he has been here just 4 weeks, finally has learned to trust us, and shows his love constantly, but moving him again may set him back to where he was just a few short weeks ago. As for whether or not we take in another foster at a later date, who knows. I might, I might not. Depends on a lot of factors, such as whether I can physically handle more than what we already have or not, but it would be a guarantee that any future fosters will move on to new homes in the end.