
Good question. Our whelping box had these round 3 sides. Basset mums can be clumsy so if it saved just one puppy, I felt it was worth building them into our box. We had a box that we made in two sections, each 4 X 4 with a floor and probably 3 foot sides (can't remember). It was made by my husband when he was able to do such things, from a pattern we found in a Basset mag. out in Canada. The one section had pig rails round 3 sides, and a low level 'front' for mum to clamber over, but which kept baby puppies in This section we had in our living room, away from the noise and bustle of the rest of the house, and the others. Once the puppies were around 3 weeks, and moving around, this section was moved into the kitchen and the second 4 X 4 section, which had no pig rails round the sides, but a hinged door to one end added. The low barrier was removed. This made a natural sleeping area (the original section) and a play/emptying area.
In fact, one of us was either right there during the 'danger' period, or within hearing distance so if a puppy was to be stuck or in trouble, we'd hear.