I tape considering 2 things:
- what i don't want to remove product from.
- what i don't want to transfer black onto my buffing pad.
And vehicles are different in considering both. Basically if there is an area i think i'll spend some time on to remove any products used i tape it up. For example, i might tape the front of doors but not the back. There are some vehicles that when you open the front door it recesses the front into the jamb or sill making it tough to get that stuff that is over the edge. That is not the case with the rear of the front door because when opened a quick swipe of the now exposed rear edge/sill/jamb is all you need. Also on my second point, i always cover black trim to avoid going over it and turning my white buff pad BLACK!
Other little things i look for are emblems, badges etc. that i certainly don't want to risk damaging or maybe tearing a nice gouge in my pad. And the only thing a seal "shut" may be the door handles. And then i tape a razor knife and slice it unsealed.
And my final point...if there is anything you are wondering about when looking around the vehicle i tape it!
Then when i'm done taping i place a large beach towel on the windshield and 4 more over the wheels/tires.
Another tip i use is i premix up a bucket of ONR and use that for any splatter, dust removal as i go along and to give the next panel a quick clean before machining.