If they want to, personally I think my guy is sexy in them and will indulge me sometimes. If they find it works for them or if they want to be sexy in them like women do when they wear thongs, really, why not?
It is not something I care to see. However, if men choose to wear them and I don't have to look at it, great! I wear a thong everyday. They are comfortable. I am sure some men find them comfortable too.