I think, personally, it's nice to have a 'few' locos with sound.
Having one rumbling on idle, or a few shunting about works very well. But at speed as they travel around, the noise of stock on the rails almost drowns them out anyway, or the whole lot gets a bit shrill and you end up doing everything in 'silent movie' mode with the noises in yer head anyway
I think for small layouts / shunting areas / dioramas, they are most effective.