Some swear by flat sheets, some swear to never use them, and will strip them off hotel beds if need be. Flat sheets and the use thereof is quite often a decision informed by culture and upbringing, though many have changed their preference to better suit their sleeping habits or circumstances.
In the US it seems that for a long time it has been common to use layered blankets, generally at least a flat sheet used as a top sheet with a bedspread above it. This is definitely necessary for those using plain wool blankets. With the more widespread use of duvets (which we Aussies more often call doonas, or what we at BLO usually label quilts) originating it seems in Europe, it is common to use a duvet cover with the same properties as a flat sheet (ie. pure cotton or perhaps flannel in winter) and to forego the flat sheet. Since the duvet cover is as easy to wash as the top and bottom or flat and fitted sheets, this results in less washing altogether, and thus uses less time, energy and water.
This does not suit everyone, however. What if your duvet cover is expensive, ill-suited to regular washing or is uncomfortable to touch though it is comfortable with respect to its warmth and weight? What if you simply dislike dressing the duvet in its cover since it’s more energy- and time-intensive than laying out a flat sheet and so would like to do it less often? You can extend the life of an expensive duvet cover or avoid redressing your duvet as often by using a flat sheet with it, since you can then wash the top and bottom sheets regularly and the duvet cover less often. Some like to dress up their beds, in which case a flat sheet strategically folded over to partially cover the duvet can be essential, along with some extra pillows for decoration.
There are many tricks out there to quickly dress a duvet, but even so it can get difficult with larger sizes, such a queen or king. There are some European countries in which it is normal for each person to have their own single-sized duvets, even when sharing a double, queen or king-sized bed – no wonder many of them have no problem quickly and easily redressing duvets.
Last but not by any means least, sleeping habits contribute not insignificantly to such decisions. Some sleepers move a lot in their sleep, and wake up with it tied around their ankles, pushed to the bottom of the bed, and so simply sleep better without it. Some find it much easier to adjust for temperature with a sheet than without, since there is less draft. On the other hand, some find it easier without the sheet due to the potential for a draft when needed. Some kick off a duvet or blanket in their sleep when they overheat, and still having the flat sheet prevents them from getting too cold on a warm night. Some need the feeling of being covered to sleep well and so choose a single flat sheet on the hottest nights for this reason. Some need not only that but also the fluffy cosiness of a doona, and so choose to sleep with a lighter summer duvet even on the hottest nights.
There’s a lot of diversity in this world and we can only hope that each person finds what sleeping arrangement best suits them 🙂