Hi, crazy little women,
In my experience horses need shoes if they are doing a lot of work on hard road surfaces, as the hoof can wear down very quickly. Also competition horses need to be shod if they are on soft ground. Competition shoes have a hole in which allows a stud to be screwed into the bottom of the shoe to stop the horse slipping.
When our last two horses were retired they weren't shod for quite a few years. The blacksmith just trimmed the hoof every 6 weeks. They had no problems at all.
I'm not quite sure what he meant by a stall. If you mean a narrow stall where the horse can't move around I agree with him. If he meant a stable I think it depends on circumstances. If horses are kept on grass all the time they can put on far too much weight, which can make work difficultSome horses suffer a severe foot problem called laminitis caused by eating too much rich grass, and need to be kept in a stable and grass limited.
The two retired horses I mentioned above spent their last few years outside and were really happy. We brought them into a stable once in that period in heavy snow and they weren't happy to be in a stable. After that they spent the rest of their retirement outside.
Hope this helps