It depends on the situation for me. I do agree with some severe situations, and as I've said before I don't think senior dogs should be treated for very much. 6 months of treatments for an extra year of life isn't worth it to me. Thing is some of these extreme cases can put a rescue on the map, and spur donations. Is it great for that dog..maybe not..but if the rescue can keep it's doors open and thus help more dogs with the extra influx of donations. Not saying it is inherently the right thing to do, but perhaps that is the thinking behind it.
I picked up a puppy off the side of the road that was in extremely bad shape the day before moving across country. I was prepared to bring the dog to be euthanized but I quickly started contacting people and a local rescue was more than happy to take her on. She recovered nicely and when I moved back I actually got to see her with her new mom. She did have lasting bone defects from poor nutrition, but, just needed treatment and some time to get to decent condition.
Pics of her the day I picked her up..
Just a few months later..
When you see the befores and afters of some of them..it kind of makes it worth it. There's also the point to where the more of a sob story a dog has, the more people that are interested in adopting and wanting to help it.