Yes, it's a habit. There are two sides to this.
Of course, there's the side that says, it's going to be used again, why bother? And there is some scientific evidence that beds that are left unmade are less likely to harbour bed bugs. The scientist that said this, said that bed bugs do not like cold, dry conditions and that by leaving the bed unmade, you made it less welcoming to these pests.
My father told me, many, many, years ago that people sweated every night in bed and that they might lose as much as a pint of sweat each night! He said that this was why a bed should be fully opened every day and left to air out for a while. After 50 years of making beds (and not only my own), I believe that he was correct. I leave my own bed fully opened for at least half an hour each day before making it, to allow any moisture to evaporate. Then I make it (or my husband does).
If you want the easiest method of making beds, I would use a fitted sheet on the bottom and a "reversible" or "two-sided" duvet cover on top. That means that in the morning, you can just fold back the duvet cover, or leave it over a chair, so the bedroom looks tidy, while still airing the bed. (Or you can just move the cover up the bed a little later in the day, so the bottom half gets aired too.) Each day, I flip the duvet cover so a different side is on view. Keeps the bed well aired.
WHY make the bed?
1. It's a good habit to get into because you can make it part of a series of habits that can get you well started into your day.
2. Once it's made, you don't want to crawl back in and untidy it again, unless you are ill
3. It leaves the bedroom tidy, so you aren't tempted to add more clutter to it and make the bed hard to get into at night.
4. As someone else has said in the comments, it makes the bed so much more inviting to get into at night, instead of having to straighten it when you're tired.
5. If you have children at home, very often the rest of the house is untidy and your bedroom can feel like a haven of peace and quiet to you. Also, if you live in a bungalow or apartment, if you have visitors, you can show them into your tidy bedroom to leave their coat and it gives them a good first impression, even if subsequently, they are going to see an awful mess elsewhere! LOL