Steven Hitchcock shows off one of his high armholes. Such armholes will allow you to lift up your arms without moving the rest of your coat. As Steven writes, “You will be in control of the coat not the other way around.”
Of course, there are other things that facilitate a comfort and movement, and it’s best not to get too fixated on armholes alone. However, whether you’re buying off-the-rack or getting something custom-made, it’s important to lift your arms a bit to see if you have a good fitting jacket. You don’t just stand in front of mirrors all day, after all, you move.
For a very interesting read about Fred Astaire’s armholes, which are kind of legendary among bespoke enthusiasts, check out this interesting article by Kerry Goodrich. Sometimes photos like this are posted when the topic of movement comes up, but as Goodrich explains, there are important trade-offs.