I don't use them at all for novices or early intermediates (typical weekly or bi-weekly progress) unless there's some kind of injury or other necessary workaround that necessitates deviation from what I'd consider to be more optimal programming.
After that, they become more useful - though I would never say strictly necessary - as a way to do assistance work that allows useful stress to be applied to targeted areas without as much systemic stress (i.e. DB press or DB bench as assistance work, IIRC Baker even likes things like lateral raises and such for already properly strong late intermediates and beyond doing hypertrophy focused blocks), or to do accessory exercises that only become more relevant later on (DB rows and such).
To reiterate: I don't think any of those things are absolutely necessary. But they're nice options to have for a late intermediate or advanced lifter. They're merely distractions - ones that have proven tempting but unproductive - for countless novices.