A useful thing is design! With it, you can several times increase the functionality of any thing. Like this stairs, for example. By itself, it is necessary in the house, but for some, children, for example, may seem boring. That's why they like to go down the railing, which the older generation usually does not approve of.
Designers offer a creative solution: equip the stairs with a slide. But since adults live in the house with children, who prefer to use a normal staircase, the slide is made folding. It can be easily decomposed by those who wish to go down, and then just as easily removed.