ITU Clip-ons vs Standard Length

Not that I really do TTs or Tris, but have a Venge, and Specialized sells two versions of clip-on aerobars (ITU legal and full extension)

I know nothing of triathlon and I may never do one in the future. I’m partial to the full extension ones, for some random UCI TT races out there. I would love to future proof to have the option of maybe doing short tris in the future.

What races could I not do with the full extension clip-ons?

Only ITU draft legal triathlon requires the shorty extensions, and many athletes skip them due to the marginal utility. Any other triathlon, including ITU non-draft legal, allow longer extensions.