The way the OP is written, I assumed it was about you (or any specific person) or an adult(ish) class.
Kids cannot be allowed to go all out unless very controlled. The vast variability in coordination alone of kids the same age, along with other markers, just doesn't allow a 'one size fits all' answer. This goes back to my previous comment about the high level of instructor control required. It is also why we have competition specific programs.
But, hopefully this may better answer your query: We spar nearly every class, every age. For kids, light contact, light gear, heavily instructor controlled. We line up the same as doing partner drill work and rotate one person every round (class size and time dependent). When kids line up with an older person/adult, they are encouraged to go harder. When lined up age equivalent, it is all about standard sparring rules. We will single out people/pairs sometimes and let them go alone. This is done for various reasons such as displaying good form (mental/physical), discussing rule/combos, bad form, or to push a kid sometimes. It is always done with a purpose.
This has never changed in my 42+ years of MA's, there is two primary TKD sparring methods: 'full' contact WT style sparring or 'tippy/tappy' extremely unrealistic point/stop sparring. The defining quality to old school points sparring is the hand speed of very specific techniques. Not particularly realistic so we have never encouraged this kind of sparring.
Yes, the three scoring
play UFO Joe rules have changed a little in WT sparring over the years but the premise is still the same.