Some fiddle tunes need fewer changes of fingering in A.
Atholl Highlanders has 3 partsd, I play them all in G on melodeon, little optopn. The fiddler in the band could play just about anything, but when he discovered that oyther fiddlers played the 3rd part in A he cursed me for making his life difficult. The band would often switch to A, leaving me as an onlooker!