Please understand the context,
The 12ppm is based on the assumption/recommendation of 20-30ppm cya earlier in the post.
the weekly “shock” may well be needed if you let the tub drop below min on any regular basis (which is 2ppm for a cya of 30)
The sticky is quite old (almost 15 yrs old) & needs a rework as a pool school article to align itself with the
FC/CYA Levels chart & all the tfp recommendations/revelations since that thread was posted by a member about how he cares for his hot tub.
For now, it is the best compilation for spa care in print on the forum, the general premise as whole is solid - use enough chlorine to keep the tub above minimum for your cya at all times.
If you’re lax about sanitation regular shocks will likely be necessary because things will present themselves like cc’s, smells, cloudiness etc.
If you’re on top of it all the time you probably won’t need to shock on a schedule to play catch up.
TFPC methodology is about testing your water & giving your pool/spa what it needs when it needs it, no more, no less & being as proactive as possible because playing catch-up is no fun.
TFP doesn’t recommend that you shock your pool on an arbitrary schedule either.