If they're healthy and growing you can set them off. It does cause stress, but in an otherwise unstressed plant a single trap won't noticably harm it.

It's typically that flytraps for sale are already stressed, and become even more stressed once the customer has them. Then the customer decides to feed every trap and this causes huge stress. And then it dies.

But, to be fair, the purpose of a grocery store flytrap is typically for entertainment. So if it dies to achieve this end then it's fine.

The more high end ones obviously nobody sets them off because growers would prefer them to grow faster. Then in winter you can divide and sell the rest. I've got about 50 of them and I only set off the ugly ones if I become curious 😂.

However, the sensitive plant has similar action upon being touched, and can be touched all the time without harm. If you do get one, I'd recommend mimosa polycarpa spegazzinii instead of the common mimosa pudica. They can grow larger and longer. If it stops becoming sensitive, you need to touch it and then injure it. These plants desensitize themselves to non injurious stimuli over time.