stemware is a fancy name for glassware with stems. holding your glass by the stem makes keeps fingerprints to a minimum and your warm fingers from the cool wine in the bowl. it also looks cool, because good manners are always stylish. however, if you need to warm your wine in a hurry, then by all means, cup with both hands and swirl.
thin-lipped glasses with large bowls are considered de rigeur in fancy establishments, but sometimes a battered bistro glass or vintage thick cut crystal is exactly what the moment requires.