I’ve pretty much always done backing vox. Luckily in the music I do it’s generally quite easy but I have found that if the bass and the vocals are doing cross melodies then it’s time to make a choice, and for me it’s what’s more important to the song, keeping the bassline as written or dumbing it down to add backing vox. Usually I’ll go with the vocals as to be honest that’s what audiences listen to most, and plenty of backing vox on a chorus really lift it imo.