She's WC but we can't entirely replicate what they'd eat or do outside. Vit A deficiencies can affect their ability to catch prey and calcium deficiencies can cause them to lose use of limbs. I've never witnessed it, but I've read many accounts herpetologists and pet owners alike that were truly awful. Never wanted to chance it. Captive toads should have vitamin d3 (important for people too), whether you take them out during the day or not.
Their exact requirements aren't known, but what can happen without supplements has been documented. Not over or under-doing it, following the guidelines, ensures you're giving her the best care possible. The longest and healthiest life you can. It can sound like a scam for overly cautious pet owners, but taking away the threat of predators won't mean anything if their health fails because of something preventable. Could be the difference between a lifespan of 5yrs or 40.
As long as supplements aren't overdone, there's little risk, only very real benefit.
My bf constantly picks on me about how much my "free" toad turned out not to cost. It's not all that much, but he's a dink. <3 The arguments for supplements are valid, and worth the cost to avoid even pricier vet bills or total premature and preventable heartbreak.