It's a habit thing.
I wear a wind-up pocket watch every day. Winding it is part of my normal routine every morning. It takes about a minute to do. Most watches will run about 35 hours on a full wind(although one of mine, an old "safety barrel" Waltham will run about 50), so it will keep running even if you forget and wind later in the day. It is good, though, to wind at about the same time every day to allow for the best time keeping.
Someone else mentioned overwinding. This is NOT an issue.
THERE IS NO SUCH THING AS OVERWINDING.
A watch should be wound until the crown is tight, and won't turn any more with a reasonable amount of force. Unless you use pliers to force the crown, you can't overwind a watch. A watch which is wound up and not running(commonly called "overwound" by those uninformed) has other problems. It could be dirty and in need of a cleaning, or there could be something more serious like a broken pivot on the balance staff or a broken roller jewel. Any of these requires a visit to a watchmaker, but are most certainly not caused by winding too tight.
At one time, dropping a mechanical watch, or any other mechanical impact, was a significant concern as it almost always resulted in a broken balance staff. All modern mechanical watches use shock protection on the balance, which greatly reduces the chance of a broken balance staff. It can still happen, though, especially with a hard enough knock.