I rug my horses in the summer, but less for appearance reasons than health reasons. One is we have a lot of insects, and bitey ones, so a rug keeps them from getting bitten. A bis issue with my old horse who used to come up in lumps.
Also, a white cotton actually keeps sun OFF them in summer, and aids with cooling, not just preventing bleaching.
In winter, myhorses work too much for it to be healthy for them to have a full winter coat. My secondary riding horses are rugged, and my main riding horse is clipped and rugged. Sometimes the secondary horses get a strip clip, just the bottom of the neck and the girth area.
If all I was doing was pleasure riding and not too hard, then I probably wouldn't rug in winter. But because I ride long, full two/three day weekend competitions, it's better for my horses health to have less of a coat.