Picnic trip to the park, good or bad?

[jncoclub]

I have a ball python, columbian redtail, hog isle and a burm- so I am posting this in both Python and Boa forums.
I have heard that nothing is better than all natural UV light from the sun to make a pet happy, healthy, and flourish. Just like humans, snakes like and really need natural light to. I have seen so many pictures of people taking their snakes out in their backyards and having them outside in general. Are their any downfalls to letting my snakes play out in the grass for a while (supervised of course)?
I don’t have my own backyard, but I am concerned that if I took one of my snakes to a park or something, that treated or fertilized grass may be a harm. I have a mite stick above my tank to prevent mites, but can they easily pick up bugs and other pests from outside? Also, is there such a thing as them getting a sense of freedom or have an instinctual sense that outside is where they want to be and therefore will be pissy or irritable being back inside and in their tanks?
I want to do what’s best for my snakes, but I don’t want to accidently do harm in the process.
So what do you all think? A picnic trip to the park, good or bad?