Unattractive and not very useful at all. Uncomfortable, infact.
Now take a look at this suit jacket from the 1920s/early 1930s with high armholes.
Vintage suits nearly always had high armholes. High armholes are cut higher under the armpit and don't deform the jacket when the arms rise. Truly high armholes might be a tad uncomfortable (tight under the armpits) at first for anyone who normally wears jackets with low armholes but they are amazed when they lift their arms and the jacket stays in place.
But high armholes are a lost art. Today practically no off-the-rack suits and very few custom jackets are made with high armholes. Perhaps this is due to the ease that low armholed jackets slip on and off (high armholed jackets are a bit more difficult, usually one arm at a time). Yet jackets are meant to be worn and if a jacket is uncomfortable or badly made (low armholes are a bad design) I do not want to wear it. I take it off. At least that part is easy thanks to the low armholes...
Low armholes are the main reason modern jackets just don't seem to fit even when they are well cut. A jacket that is perfectly shaped to your body will still feel weird and wear wrong if it has low armholes. Hopefully the pendulum will swing back to high armholes like back before armholes went bad in the 1960s.
That's why Gene Kelly and Fred Astaire were able to dance around all day and still be comfortable in their suits. It's all in the armholes.