isn't wood paneling full of nasty chemicals?

Yes, but some chemicals used in woodwooking are child safe after 30 days of curing.
The wood panels are IMO about 1/8 to 3/16 thick & will not rot for 24 to 36 months, maybe longer.
They could be used as retaining walls on the edge, turn the sealed side out, so the sun UV rays can break them down.

Wood paneling is plywood and for years the adhesives used to glue the plys together used formaldehyde to help cure them and make them waterproof. Many of these gassed off over time and in some people caused health problems. The manufacturers today have found other materials to use so your wood paneling, depending on age, may be free of formaldehyde. However there are other things you may not want to put in your soil, one of the reasons why construction materials are, usually, by law sent to hazardous materials landfills and not those that accept household trash.

I worked in a cabinet shop spray room. If this is not at least forty years old it will sit down there a LONG time.

Water will not pass through it.

If it is the old type fishished with oil, or even varnish, it will still be down there a long time.

Ahh thanks everyone, Looks like it's headed to the dump then.

I'm in favor of landfilling it, because it is just a little too far towards the trashy side of things to put in the garden, in my opinion.

But by and large, construction materials are not hazardous waste that have to go to a special landfill. In fact, C&D (construction and demolition) landfills actually have lower construction standards than sanitary landfills where your garbage goes. Mainly because there is less putrescible stuff to create leachate. Sanitary landfills are in the middle of the spectrum, and they can take C&D. Haz waste landfills have very stringent standards. The only demo waste that I see going to haz waste landfills is lead paint sandblasting waste, because it fails the RCRA (TCLP) leachability test.

A homeowner can even put small amounts of asbestos at the curb, properly packaged and labeled. Homeowners can do all kinds of stuff that is way more of a hassle for a business.

What about between my raised beds? and then covered with a heavy mulch? Still too much risk of it leaching in underneath the beds? In the paths I don't care if it takes years to break down.

Also, the paneling is about 15 years old.

What would you use it for between the beds, a path?

It is not going to leach anything worth concern, paranoia is more of a concern with many items than what it actually does to anything.
It would make a good path base for years.

I agree with that. I've used ratty pieces of OSB and such in my garden paths.

I like finding a second use for things instead of putting them in a landfill, so if leaching toxins into the ground is not a concern, I think I'll use them for a base between my beds. I planned on mulching or stoning them, so I can use it as a weedblock and I won't have to get landscape fabric or pile tons of extra cardboard. I have enough cardboard for my bed liners, but probably not if I had to line the beds and the paths prior to mulching.

I might as well go full monty on the dang things and mulch and trim the whole area with landscape timbers. That way I can keep the edge neat and not sweep up mulch with my mower or weed whacker. They have them for $4 for an 8 footer right now at the orange colored big box, Maybe cheaper at my local lumber yard. Do it once and keep maintenance low, seems to be the motto many adhere to.

Putting sheets of paneling on the ground is an invitation to rodents. I sympathize with your desire to keep them out of the landfill, but sometimes that's the best place for items that have outlived their usefulness.

Well I am trying to encourage Garder snakes, would that attract them as well? Maybe they will eat the baby rodents and then also all my slugs? Haha

I put down all kinds of shelving/countertop/paneling/wood product odds and ends as a 'ground cover' around my firewood pile, and I've found it helps keep the weeds down, disintegrates eventually, and can't be too toxic given the enormous number of diverse wee critters I find under it all.

I'd use it for garden paths between your beds, and not worry about it.

I'm curious why mice would be drawn to a place with a sheet of wood under the mulch more than a place with just mulch. I find them in the compost bin anyway. The cat can catch them out in the lawn.