It was also used for formally entertaining guests and wedding receptions. It was where the expensive furniture and good dishes were kept, that you didn't really use except when trying to impress people. So yes, it wasn't for families who lived in a one room, dirt floor hovel, or families that had servants and many formal entertaining rooms that they could afford to use regularly and maintain, but if you were middle class and had enough for a "good room" that you wanted to "save for best" then that was what it was used for. https://www.simplysoldaz.com/the-death-room/

Also- 30% of people died before the age of 5 in 1900 England and USA, so it's not like they rarely had occasion to use it.

There's a part in one of the Disc World books by Terry Pratchett (which are fiction, but roughly analogous to that time period in England) where we are being introduced to Granny Weatherwax (a witch) and it is said of her that she never ever uses the front door of her own house, because that is for brides and corpses and she didn't plan on ever being either of those.

My parents grew up in working class 1950s Britain. My dad's parents slept in the kitchen (with a curtain round the bed for privacy), which was also the room that most "living" was done. The three kids shared a single small room, with both teenage boys sharing a double bed, their older sister got her own single bed, and she stayed there until she married and moved out in her early twenties. I remember seeing that room and even as a child it seemed cramped, no space really for anything else once the two beds were in it.

While the whole the family was living, eating and sleeping in two small room, an immaculate "front room" / parlour was kept solely for the two or three days a year where they had "company" (a family event like a wedding or funeral, or the priest visiting or something). The front room was bigger than both the others. It's hard to comprehend the priorities that led to this sort of thing, but it was apparently extremely common in that time and place.