music help: Music theory and such - Help.com

I dont know violin but if the shift sounds good to your ears use it unless it is harder to play

OK being a guitarist that plays guitar like a violin I can say it is always best to practice in as many keys as possible.. This will develop your ear and allow you to master unusual hand and finger gymnastics…For me playing the difficult keys makes me a better player

I’m a violinist (hah, that sounds nerdy) and yeah, the only reason I can think of at the moment, is F sharp is easier to play than A flat, because you can use open strings instead of the 4th finger, but you’ve already said that :)
I’ll keep on thinking :)

Most instrumentalists that I know would rather play sharps than flats anyhow. On Away in a Manger (Key of G) I always add in Em too. The difficulty for instruments that cannot be capo’d, is that if you are accompanying a vocalist, you have to be a lot more versatile to be able to play the key they want to sing in. Mandolin and violin are the same so sometimes you can steal some ideas from other instrumental method books.