My daughter and SIL take a Shemagh on trips. These bits of cloth have proved very useful as a ground cloth for picnics and recently as a sling for a fractured limb in a Fairbanks snowmobile accident. Since they have many uses, it may be a good idea to pack one.
Yes, a shemagh, pareo, sarong, any length of fabric is useful. Something big enough to be used as a wrap skirt will solve the problem of no trousers, or no knees in places of worship, but I do prefer something without all the tassles that some shemagh have.
Design or style may be personal preference or style esthetic.
I added a cranberry colored pashmina to my packing list in 2019 because sometimes I’m slightly cold on a train or plane. I also used it as a warmer decorative scarf for dinner at night, if needed. It could probably work as an arm sling, too.
It's definitely a good idea to pack some kind of rectangular piece of cloth -- a shemagh/keffiyeh, a pashmina, or a sarong. It depends on the destination.
I took a keffiyeh to Egypt last year. After I got it, I became concerned when I started reading that it was considered cultural appropriation for white folks to wear a keffiyeh, especially a Palestinian-made keffiyeh. I packed it anyway. I wore it frequently, and especially appreciated it when we ran into a serious dust storm in Luxor. Nobody complained and it garnered lots of complements. Fortunately, I never had to use it as a sling.
I almost always pack a real cashmere pashmina, which serves as a blanket on the plane and a warm wrap in the evenings.
Sarongs can be handy, but I probably need to drop a few pounds to look my best in a sarong. :-) I do use them as a swimsuit coverup.
After reading the Hitchhiker's Guide to the Galaxy way back in the day, I know it is important to have a towel at all times! I always take a cloth with me, call it what you will. And sometimes I buy them along the way, too!