It depends.
If DSP is on, you get a bang. If it's off, you won't.
So, If I am expecting a bang because I saved and DSP is off, it just bugs me that no bang is sent :)
If, say, you want to send one and only one bang to [switch~] so as to graph tables when DSP starts, then [r pd-dsp-started] is only useful if you spigot-out future bangs/saves/etc, otherwise you are graphing tables on every save...
It's a feature if you use it for randomness, say, to randomize seeds according to when dsp on/off switching or graph redrawing falls, say linked with a [timer] object :)
Perhaps [r pd-dsp-started] should only send bangs when dsp starts or stops, and not when the dsp graph is redrawn.
In any case, I think it's the misnomer what's confusing me. I realize that saving redraws the dsp graph, but I don't see why the dsp would "start" if it was already switched "on", even though I do understand that, for a tiny moment, the dsp needs to be off behind the scenes.