My immediate family used bathrobes when I was growing up, and my parents still do. I own one, but rarely use it for its intended purpose.
You’re supposed to throw on a bathrobe when you get up in the middle of the night to pee and/or eat that last slice of pie in the fridge. Because your pajamas are practically UNDERWEAR, and it would just be too embarrassing to be seen in your PJs, even by your parents/children. For kids’ sleepovers, bathrobes are essential. Bathrobes are also handy if your house is chilly, and your PJs are warm enough while you’re under the covers, but too cold when you wander around the house. I usually use my bathrobe for this. I also use it for when I’m not sleeping at home, because I customarily sleep in just my panties, and most people just would rather that I cover up if I need to make that potty run. Usually I use it if I need to stay in the hospital, because I really don’t think those gowns do a good job of covering me up. While I don’t care if complete strangers see me in my skivvies, most of those strangers would prefer to be spared that sight.
A bathrobe is also a good idea for when the house catches on fire in the middle of the night…you’re dressed enough that you won’t be cited for public lewdness, but they’re very easy to grab and toss on when you’re in a hurry.